Altered Python interactive interpreter subprompt (sys.ps2) to use an
object so its length will change dynamically as the history grows; took
the opportunity to tidy and document .python a bit.

Also added a script I hadn't written, to update the pkgfile database.

--HG--
extra : amend_source : fca21c9f0df83b4e6cffcf3aa3e69a1f2330e149