Merge branch 'ng/cleanup-revamp' into ng/master

* ng/cleanup-revamp:
  [ng] cleanup: merge '%compile_clean_files' in '%clean_files'
  [ng] clean: drop minor DOS-related cruft in libtool support
  [ng] cleanup: remove 'clean-hdr.am'
  [ng] check: keep cleaning of '.log' and '.trs' files near other rules
  [ng] cleanup: remove 'libtool.am'
  [ng] refactor: prefer '&file_contents' over '&file_contents_internals'
  [ng] cleanup: merge '%compile_clean_files' in '%clean_files'
  [ng] refactoring: no "cleaning" rules in compile.am
  [ng] clean: don't remove object files in '.' unconditionally
  [ng] cleanup: remove 'depend.am'
  [ng] refactoring: move definition of $(am__mv) in depend2.am
  [ng] automake: new global variable '%clean_dirs'
  [ng] clean: do not ignore errors while removing files
  [ng] clean: revamp recipes and APIs to extend cleaning rules
  [ng] clean: simplify cleaning of compiled objects
  [ng] deptrack: clean depdirs using *clean-am targets
  [ng] deptrack: remove an obsolete comment

diff --cc Makefile.am
Simple merge

diff --cc lib/am/distdir.am
Simple merge

diff --cc lib/am/parallel-tests.am
Simple merge

diff --cc syntax-checks.mk
Simple merge