[FYI] Merge branch 'maint' into master

[Stefano Lattarini]

Merge branch 'maint'
    
    * maint:
      fix: make a test script executable
      coverage: expose automake bug#9651
      parallel-tests: automake error our on invalid TEST_EXTENSIONS
      fix: regenerate Makefile
      docs: don't suggest installing `.m4' files in hard-coded location
      distuninstallcheck: fail also when only one file is left installed