gnome-vfs configure fails to complete in extension modules in the absence of
"bzlib.h".  Environments without a system-installed "bzlib.h" will fail to
build modules like "audio/gnome-vfs-cdda" with the following:

checking for bzCompressInit in -lbz2... no
checking bzlib.h usability... no
checking bzlib.h presence... no
checking for bzlib.h... no
configure: error: Gnome-vfs requires libbz2 to compile.
*** Error code 1

To fix this, promote bzip2 dependency from gnome-vfs/Makefile to
gnome-vfs/Makefile.common.

XXX Only /usr/pkg/lib/gnome-vfs-2.0/modules/libbzip2.so actually appears to
link with libbz2.so, so it's possible that configure is being overly picky.

(dsainty)