[Telepathy] Making Vala a hard build-dep for Folks

[Travis Reitter]

For most of Folks' lifetime, we've shipped the C files that valac
generates. The main purpose was to make life easier for developers and
packagers who didn't want to hassle with bleeding-edge versions of
gobject-introspection and vala (which may not have been pre-packaged).

Shipping these generated files has resulted in an extra-complicated
build system and I lost track of the number of times I had to un-break
'make distcheck' just before a release as a result. The latest incident
related to shipping generated files resulted in a major bug [1].

We made gobject-introspection a hard build dependency a while ago
without any complaints that I'm aware of. And Vala has been a hard build
dependency for non-releases for even longer (again, with no complaints).

Vala 0.14.0 (which is slightly newer than the version we require,
0.13.4) is available in Debian testing, Ubuntu 11.10 and Fedora 16.

Does anyone have objections to Folks making Vala a hard build
dependency? (Vala is not/cannot be a runtime dependency, so this should
only potentially affect packagers.)

The only downside I foresee is this will require Folks to delay using
Vala features until they've been widely available for longer (and the
fact that Folks and Vala both track the Gnome release schedule should
minimize this impact).

Thanks in advance for any input,
-Travis

[1] https://bugzilla.gnome.org/show_bug.cgi?id=662274#c18