New optional parameter "keyfile" for ssh transport allows the user to select
the private key to be used to authenticate to the remote host.

In preparation for a future patch adding new virFile APIs.

* src/util/files.h, src/util/files.c: Move...
* src/util/virfile.h, src/util/virfile.c: ...here, and rename
functions to virFile prefix.  Macro names are intentionally
left alone.
* *.c: All '#include "files.h"' uses changed.
* src/Makefile.am (UTIL_SOURCES): Reflect rename.
* cfg.mk (exclude_file_name_regexp--sc_prohibit_close): Likewise.
* src/libvirt_private.syms: Likewise.
* docs/hacking.html.in: Likewise.
* HACKING: Regenerate.

* src/rpc/virnetclient.c: Skip close attempt if virNetClientPtr
  is NULL

Since the I/O callback registered against virNetSocket will
hold a reference on the virNetClient, we can't rely on the
virNetClientFree to be able to close the network connection.
The last reference will only go away when the event callback
fires (likely due to EOF from the server).

This is sub-optimal and can potentially cause a leak of the
virNetClient object if the server were to not explicitly
close the socket itself

* src/remote/remote_driver.c: Explicitly close the client
  object when disconnecting
* src/rpc/virnetclient.c, src/rpc/virnetclient.h: Add a
  virNetClientClose method

When unregistering an I/O callback from a virNetSocket object,
there is still a chance that an event may come in on the callback.
In this case it is possible that the virNetSocket might have been
freed already. Make use of a virFreeCallback when registering
the I/O callbacks and hold a reference for the entire time the
callback is set.

* src/rpc/virnetsocket.c: Register a free function for the
  file handle watch
* src/rpc/virnetsocket.h, src/rpc/virnetserverservice.c,
  src/rpc/virnetserverclient.c, src/rpc/virnetclient.c: Add
  a free function for the socket I/O watches

* src/rpc/virnetclient.c: Add debugging of ref counts

If we get an I/O error in the async event callback for an RPC
client, we might not have consumed all pending data off the
wire. This could result in the callback being immediately
invoked again. At which point the same I/O might occur. And
we're invoked again. And again...And again...

Unregistering the async event callback if an error occurs is
a good safety net. The real error will be seen when the next
RPC method is invoked

* src/rpc/virnetclient.c: Unregister event callback on error

If the server succesfully validates the client cert, it will send
back a single byte, under TLS. If it fails, it will close the
connection. In this case, we were just reporting the standard
I/O error. The original RPC code had a special case hack for the
GNUTLS_E_UNEXPECTED_PACKET_LENGTH error code to make us report
a more useful error message

* src/rpc/virnetclient.c: Return ENOMSG if we get
  GNUTLS_E_UNEXPECTED_PACKET_LENGTH
* src/rpc/virnettlscontext.c: Report cert failure if we
  see ENOMSG

Set StrictHostKeyChecking=no to auto-accept new ssh host keys if the
no_verify extra parameter was specified.  This won't disable host key
checking for already known hosts.  Includes a test and documentation.

Gnulib finally learned how to do pthread_sigmask on mingw.

* .gnulib: Update to latest, for pthread_sigmask.
* bootstrap.conf (gnulib_modules): Add pthread_sigmask.
* configure.ac (AC_CHECK_FUNCS): Drop redundant check.
* src/rpc/virnetclient.c (virNetClientSetTLSSession)
(virNetClientIOEventLoop): Make code unconditional.
* src/util/command.c (virFork): Likewise.
* tools/virsh.c (doMigrate, cmdMigrate): Likewise.

Coverity noted that 4 out of 5 calls to virNetClientStreamRaiseError
checked the return value.  This case expects a particular value, so
warn if our expectations went wrong due to some bug elsewhere.

* src/rpc/virnetclient.c (virNetClientCallDispatchStream): Warn on
  unexpected scenario.

Detected by Coverity.  Both are instances of bad things happening
if pipe2 fails; the virNetClientNew failure could free garbage,
and virNetSocketNewConnectCommand could close random fds.

Note: POSIX doesn't guarantee the contents of fd[0] and fd[1]
after pipe failure: http://austingroupbugs.net/view.php?id=467
We may need to introduce a virPipe2 wrapper that guarantees
that on pipe failure, the fds are explicitly set to -1, rather
than our current state of assuming the fds are unchanged from
their value prior to the failed pipe call.

* src/rpc/virnetclient.c (virNetClientNew): Initialize variable.
* src/rpc/virnetsocket.c (virNetSocketNewConnectCommand):
Likewise.

When the remote client receives end of file on the stream
it never invokes the stream callback. Applications relying
on async event driven I/O will thus never see the EOF
condition on the stream

* src/rpc/virnetclient.c, src/rpc/virnetclientstream.c:
  Ensure EOF is dispatched

If a streams error is raised, virNetClientIOEventLoop
returns 0, but an error is set. Check for this and
propagate it if present

* src/rpc/virnetclient.c: Propagate streams error

To facilitate creation of new clients using XDR RPC services,
pull alot of the remote driver code into a set of reusable
objects.

 - virNetClient: Encapsulates a socket connection to a
   remote RPC server. Handles all the network I/O for
   reading/writing RPC messages. Delegates RPC encoding
   and decoding to the registered programs

 - virNetClientProgram: Handles processing and dispatch
   of RPC messages for a single RPC (program,version).
   A program can register to receive async events
   from a client

 - virNetClientStream: Handles generic I/O stream
   integration to RPC layer

Each new client program now merely needs to define the list of
RPC procedures & events it wants and their handlers. It does
not need to deal with any of the network I/O functionality at
all.