multiple vala versions in 3.4

[Colin Walters <walters verbum org>]

Hi,

Looks to me like some modules in the 3.4 moduleset want Vala 0.15 c.f.
this commit:

commit e6e59801cd13f5fa02ca7bbf6d269db886aca9f4
Author: Frédéric Péters <fpeters 0d be>
Date:   Mon Jan 9 16:48:46 2012 +0100

    3.4: bump vala to 0.15 (required by gnome-boxes and dconf, at least)


But others (folks at least) fail to compile with 0.15.  So far we've
been relying on the fact that the .c files are cached in the tarball for
folks, but this is pretty broken.  Jhbuild is supposed to to be the
developer tool where you can actually hack on stuff.

I think we need to take both Vala 0.14 and 0.15 in the moduleset, using
the --disable-unversioned flag.

However, modules will need to be patched to find the correct valac and
vapigen with the -0.14 suffix.  For example, folks just does:

        AC_PATH_PROG([VAPIGEN], [vapigen], [])
        if test "x$VAPIGEN" = "x"; then
              AC_MSG_ERROR([Vala must be built with --enable-vapigen])
        fi

We could manually pass VALAC=valac-0.14 VAPIGEN=vapigen-0.14 to
configure, but it's probably better to fix this inside the configure
scripts.

Jürg, do you agree we should use --disable-unversioned for vala in
jhbuild?  This is what Ubuntu appears to do.  As far as I can tell
Fedora just accepts the generated .c files.

(Or perhaps more ideally, modules using 0.14 would port, but if we're
going to keep having Vala rebases, we should sort this out better)