An Interactive Repy Console.

(Moved from a proposed pull request to SeattleTestbed/repy_v2 where
it definitely did not fit.)
This is meant for people like me who are too lazy to manually import
`repyportability` etc. for interactive testing and development.
NOTE: It is *not* an attempt to drop to an interactive Python
interpreter when a Repy program encounters an exception. I'm working
on this in a separate branch.
Make repyportability changedir to the location it is in before attempting dylinking in stuff.

This is required as dylink cannot access "outside" locations, i.e. any
other place than the dir it is located in. Note that I assume that
repyportability and dylink are in the same dir!