uninstall: "make uninstall" before "make install" works

uninstall: "make uninstall" before "make install" works

This change fixes automake bug#9578.

* lib/am/inst-vars.am (am__uninstall_files_from_dir): New internal
macro, that defines a shell code fragment to uninstall files from
a given directory.
* lib/am/data.am (uninstall-%DIR%%PRIMARY%): Use it, to reduce code
duplication and improve consistency and correctness.
* lib/am/libs.am (uninstall-%DIR%LIBRARIES): Likewise.
* lib/am/lisp.am (uninstall-%DIR%LISP): Likewise.
* lib/am/mans.am (uninstall-man%SECTION%): Likewise.
* lib/am/python.am (uninstall-%DIR%LIBRARIES): Likewise.
* lib/am/scripts.am (uninstall-%DIR%SCRIPTS): Likewise.
* tests/uninstall-pr9578.test: New test.
* tests/uninstall-fail.test: New test.
* tests/Makefile.am (TESTS): Add them.
* NEWS, THANKS: Update.

Report by Nick Bowler.