Merge branch 'maint' into branch-1.11

Merge branch 'maint' into branch-1.11

* maint:
  gitattributes: custom merge driver for ChangeLog not needed anymore
  gitattributes: use "union" merge driver for NEWS
  tests: fix a timestamp-related spurious failures
  dryrun: fix regression with '$(am__make_dryrun)'
  test defs: function 'is_newest' now works also with directories
  refactor: new variable telling whether make is running in "dry mode"
  tests: do not clobber the modified CC
  tests: put AM_PROG_CC_C_O before AC_OUTPUT to help losing compilers