Add a script-only idmap module.

Add a script-only idmap module.

In this third version I have cleaned up some unused variable warnings that
only the Samba 3 build found and added a man page based on the idmap_tdb2
man page. I have also added support for ID_TYPE_BOTH mappings and replaced
calls to popen with something safer. Also, I removed some non-PC macros.

Signed-off-by: Richard Sharpe <rsharpe@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu Jan  8 04:30:32 CET 2015 on sn-devel-104