Fix for distcommon2.test:

Fix for distcommon2.test:
* automake.in (automake_needs_to_reprocess_all_files): New
variable.
("main"): Process all Makefiles a second time if
$automake_needs_to_reprocess_all_files is set.
(maybe_push_required_file): Return 1 or 0 whether the file is
pushed or not.
(require_file_internal): Set $automake_needs_to_reprocess_all_files
if an added file can't be pushed.

* test/distcommon2.test: New file.
* test/Makefile.am (TESTS): Add distcommon2.test.
From Pavel Roskin.