Merge branch 'maint'

Merge branch 'maint'

* maint:
  tests: do not assume the object file extension is .o
  tests: avoid spurious failure of 'transform2.test' on Cygwin
  tests: avoid spurious failure of deleted-am.test with FreeBSD make
  tests: avoid possibly undeserved PASS from check8.test
  warnings: more precise category and message for one warning
  release: revamp rules to tag and upload the releases
  amversion: add missing dependency
  hacking: update advice w.r.t. synced files
  hacking: don't reference ChangeLog anymore

+ Extra non-trivial edits:

* tests/suffix8.tap: Copy in (by hand) the modifications done
to 'suffix8.test' on maint, i.e., the addition of an explicit
'.y_.obj:' suffix rule to Makefile.am.