package/vala: also wrap vapigen

package/vala: also wrap vapigen

when compiling gobject-introspection .gir files, some packages use vapigen to
generate a vala-api compatible .gir file. These packages tend to call vapigen
directly instead of vala or valac.

Without the wrapper, building the .gir files fail. In the case of for example,
gupnp-dlna throws the following error:
"error: Package `Gst-1.0' not found in specified Vala API directories or
GObject-Introspection GIR directories."

Installing the vala wrapper for vapigen fixes the above issue.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>