depend: refactor and remove code duplication * lib/am/depend2.am: Here. The obsolescent comments removed from this same file in commit 'v1.13.1-42-g8f06bfb' of 2012-01-09, "depend2.am: fix comments on verbosity of compilation rules", gave the rationale for why that code duplication was there in the first place (rationale that, like those comments, has been obsolete by the silent-rules introduction). * bin/automake.in: Given the refactoring in 'depend2.am', there is no longer need to add extra trailing whitespace to the entries of the '%sourceflags' hash (which are used for the '%SOURCEFLAG%' transform when 'depend2.am' is processed. * t/fort2.sh: Adjust to avoid spurious failures. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>