pkg-config: present API version and not package version

This way PKG_MODULE() autoconf test checks for required API
rather than release version (e.g required API could be in all
all of 3.4.5, 3.5.1, 3.6.4 etc.)

With the first "release" of gfapi, the current version (4) will
be frozen.

Version 3 is sufficient for QEMU's requirement. Version 4 is
necessary for Samba VFS

Change-Id: Iada3a4c88b9c67413dcd57004fd8a62926a21b42
BUG: 953694
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5165
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
gfapi: ignore NULL and -1 parameters in glfs_set_logging()

Permit changing either logfile or level by specifying the other
as -1 or NULL respectively.

Change-Id: I7df05db7b613c57e0106a5cce846ae26d2a160d4
BUG: 953694
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5166
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Xavier Hernandez <xhernandez@datalab.es>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>