[PATCH] Supporting shtool within automake

[Bonzini]

This patch, relative to automake 1.5, adds support for shtool in automake.
By specifying --shtool, automake does not require anymore mdate-sh,
install-sh and mkinstalldirs, and instead uses the corresponding shtool
scriptlets mdate, install and mkdir (which supports portably the -p
argument).  Creation of shtool when --add-missing is specified is demanded
to shtool's `shtoolize' script and can be customized with the other new
option, --include-shtool=SCRIPTS.

Passes the test suite with no regressions.  A small change was necessary in
texi-vers.am as well (because the file name for mdate-sh now is not fixed
anymore).  Autoconf already supports shtool in AC_PROG_INSTALL.

The patch documents all these new features in automake.texi as well

Paolo Bonzini