* vala-work:
vala: improve comments to AM_PROG_VALAC
news: update w.r.t. recent vala changes
vala: if no proper compiler found, set $(VALAC) to 'valac'
vala: AM_PROG_VALAC should not produce an error for tool-old valac
docs: document recent changes to AM_PROG_VALAC
tests: enhance tests on AM_PROG_VALAC
vala: style fixes in vala.m4
vala: add action arguments, for when no proper vala compiler is found