scripts: add sed expression to apply when renumbering patches

Some patchsets have superfluous members in their names (eg. the ones coming
from Gentoo), so it can come in handy to pass a sed RE to strip them out of
the final patch name.
Also add a 'fake' mode, where the command will only be printed and not
executed, so we can check beforehand if the rename will be OK.

This is NOT the official version of dialog.  This version has been

significantly modified from the original.  It is for use by the Linux

kernel configuration script.  Please do not bother Savio Lam with 

questions about this program.