We can't use GNULIB's fprintf-posix due to licensing
incompatibilities. We do already have a portable
formatting via virAsprintf() which we got from GNULIB
though. We can use to create a virFilePrintf() function.

But really gnulib could just provide a 'fprintf'
module, that depended on just its 'asprintf' module.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

It may shorten the code a bit as the following pattern:

  VIR_STRNDUP(dst, src, cond ? n : strlen(src))

is used on several places among our code. However, we can
move the strlen into virStrndup and thus write just:

  VIR_STRNDUP(dst, src, cond ? n : -1)

The surest way to avoid regressions is to test documented behavior :)

* tests/virstringtest.c (testStrdup): New test case.
Signed-off-by: NEric Blake <eblake@redhat.com>

The source code base needs to be adapted as well. Some files
include virutil.h just for the string related functions (here,
the include is substituted to match the new file), some include
virutil.h without any need (here, the include is removed), and
some require both.

This introduces a few new APIs for dealing with strings.
One to split a char * into a char **, another to join a
char ** into a char *, and finally one to free a char **

There is a simple test suite to validate the edge cases
too. No more need to use the horrible strtok_r() API,
or hand-written code for splitting strings.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>