glusterfs-api.pc: include pkgconfig file in -devel RPM
    
    From: http://review.gluster.com/3665 & http://review.gluster.com/3693
    
    Other projects (like Samba) use pkg-config to discover support for
    GlusterFS and gather the CFLAGS and LDFLAGS for compiling against
    libgfapi.so.
    
    Not building new packages now, only making sure it is included in the
    next run.