* added some tests for implied and conflicting options
* make all Session objects inherit from the base session
* small cleanups with respect to test setup
* separate tests a bit
--HG--
branch : trunk
of most of the pkgdir and changed to use get_collector_trail.
Some tests need to be rewritten or killed, right now they're skips.
There are no checks (yet) whether this works with topdir being something
else than previous pkgdir, we'll see...
--HG--
branch : trunk