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.

reporter_name="Yann E. MORIN"

reporter_url="http://ymorin.is-a-geek.org/dokuwiki/projects/crosstool"

reporter_comment=""