vala tests: avoid spurious failure with older GObject * t/vala2.sh: In the 'PKG_CHECK_MODULES' call in 'configure.ac', don't require gobject >= 2.10, but just >= 2.4: that is enough in order for the test to pass. * t/vala3.sh: Likewise. * t/vala5.sh: Likewise. Also, skip the test instead of failing if the ./configure invocation fails: that is likely due to the fact that the GObject library is too old or missing, and that is not automake's fault. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>