LIBVIRT_ARG_WITH_ALT is more generic than LIBVIRT_ARG_WITH, which
is tailored at switching features on and off.

Rename the macros according to their intended purpose, and add
some documentation to help developers pick between the two.

Usage of AC_REQUIRE will mess with order how LIBVIRT_CHECK_* macros
are composed into configure.ac.  This ensures that the output of
configure --help is properly ordered and grouped into sections.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Following patch will update LIBVIRT_CHECK_(LIB|LIB_ALT|PKG) macros in
a way that you will be able to call a another macro as a fallback if
the first one fails.  To allow that, we need to move the
LIBVIRT_ARG_WITH out of those macro to not have two or more same lines
in output of "configure --help".
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

${exec_prefix} and ${prefix} point to the same directory in
most setups, but when that's not the case the former should
be used for architecture-dependent data such as shared objects,
which makes it the best fit for our Wireshark dissector.

While at it, change all uses of $(var) to ${var}: they are
absolutely identicaly as far as make's concerned, but autoconf
itself seems to prefer the latter form so we might as well
follow suit.

We only need to strip $ws_prefix from $ws_plugindir if we've
retrieved it from pkg-config: if we're building it ourselves
from $libdir, we can just use it without further processing.

Since we're using autoconf to substitute the right value in
Makefile.am now, we can use a less generic name without running
into circular dependencies.

Adding $(prefix) in Makefile.am, as we were doing, means that
it would be prepended even when using --with-ws-plugindir,
which is something we don't want to happen.

Instead, we add it beforehand but take care that it doesn't
get expanded until make is called.

Even when we're building $plugindir ourselves because we can't
retrieve it using pkg-config, we still want to strip the prefix,
except in that case it would be the same prefix we're using for
building libvirt.

The fact that $plugindir is missing also doesn't tell us
anything about $ws_prefix, so we have to handle the two variables
separately.

Keep all variable declarations close together.

Use a separate variable instead of setting it inline for
slightly cleaner code.

The autoconf manual says we shouldn't be using this variable (and
some others) outside of Makefiles as it prevents users providing
their own prefix at the installation phase.

https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Installation-Directory-Variables.htmlSigned-off-by: NMichal Privoznik <mprivozn@redhat.com>

So, when building wireshark plugin, we get the plugindir variable
from the wireshark.pc as well as prefix. Then we replace the
prefix in the plugindir with our own prefix where libvirt is
building to:

  plugindir="${prefix}${plugindir#ws_prefix}"

However, as you can see, there's '$' missing in front of the
ws_prefix variable. This results in the mangled plugindir, for
instance like this:

  plugindir='/usr/usr/lib64/wireshark/plugins'
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

Our distcheck is broken. Well, it works but only by pure chance.
When wireshark plugin is enabled, we try to query which path
should the plugin be installed into. Firstly, we try to ask
pkg-config as some releases of wireshark already sets
corresponding variable in their pkg-config files. However, if we
obtained no value from there we try to construct the path on our
own. Based on our observations it usually is:
$libdir/wireshark/plugins/$version/.
Now, the problem is in the way we are deciding whether we have
obtained the plugin directory from pkg-config or not. Simply
said, we are checking wrong variable. The variable we are
checking has never been set, thus in our test is empty and
therefore we will always construct the plugin dir path on our
own, regardless of its presence in the pkg-config file.
To make things worse, after fixing this problem, VPATH build was
broken as it now tried to install plugin into correct directory.
Yes, this is problem, because --prefix was not honoured and
everything but the plugin was installed into given prefix. I've
managed to resolve this issue by replacing plugin dir prefix with
our own. So when doing regular installation (our prefix ==
wireshark prefix), nothing changes. When doing VPATH build &
installation plugin is installed into correctly prefixed dir.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

Like everything we install, it should be prefixed with DESTDIR.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

There has been a report on the list [1] that we are not
installing the wireshark dissector into the correct plugin
directory. And in fact we are not. The problem is, the plugin
directory path is constructed at compile time. However, it's
dependent on the wireshark version, e.g.

  /usr/lib/wireshark/plugins/1.12.6

This is rather unfortunate, because if libvirt RPMs were built
with one version, but installed on a system with newer one, the
plugins are not really loaded. This problem lead fedora packagers
to unify plugin path to:

  /usr/lib/wireshark/plugins/

Cool! But this was enabled just in wireshark-1.12.6-4. Therefore,
we must require at least that version.

And while at it, on some distributions, the wireshark.pc file
already has a variable that defines where plugin dir is. Use that
if possible.

1: https://www.redhat.com/archives/libvirt-users/2015-October/msg00063.htmlSigned-off-by: NMichal Privoznik <mprivozn@redhat.com>

Wireshark supports pkg-config since 1.11.3.  Right now we build
wireshark-dissectior tool as default trough rpm build only on
fedora >= 21 and there is new wireshark that supports pkg-config.
If someone wants to build libvirt with wireshark-dissector against old
wireshark, they should specify the location by hand.

This patch is mainly to fix wrong dependency on wireshark binary as it
doesn't make sense to require that binary file to just get version info
of that package in makefile.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>