* automake.in (handle_configure): Distribute and define mkinstalldirs

* automake.in (handle_configure): Distribute and define mkinstalldirs
only if it is already present in the package.
(scan_autoconf_files): Do not require mkinstalldirs.
(require_build_directory): Use $(mkdir_p), not $(mkinstalldirs).
* lib/am/data.am, lib/am/distdir.am, lib/am/install.am,
lib/am/java.am, lib/am/libs.am, lib/am/lisp.am, lib/am/mans.am,
lib/am/progs.am, lib/am/python.am, lib/am/scripts.am,
lib/am/texinfos.am: Use $(mkdir_p) instead of $(mkinstalldirs).
* m4/mkdirp.m4: New file.
* m4/Makefile.am (dist_m4data_DATA): Add mkdirp.m4.
* m4/init.m4 (AM_INIT_AUTOMAKE): Call AM_PROG_MKDIR_P.
* tests/Makefile.am (TESTS): Remove insh.test.
* tests/insh.test: Delete.
* tests/defs.in, tests/instsh.test: Do not install mkinstalldirs.
* tests/auxdir.test: Install mkinstalldirs.
* tests/distdir.test, tests/instman.test, tests/pr2.test: Use
$(mkdir_p), not $(mkinstalldirs).
* tests/empty.test: Run configure, do not substitute things by hand.
* doc/automake.texi (Optional) <AC_CONFIG_FILES>: Take install-sh
as an example, not mkinstalldirs.
(Auxiliary Programs) <mkinstalldirs>: Update.