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>
(cherry picked from commit 76c1fd33)
Signed-off-by: NEric Blake <eblake@redhat.com>

Conflicts:
	tests/Makefile.am - several intermediate tests not backported