this merge contains:
* a new plugin architecture
* a pluginized pytest core
* many pytest related refactorings
* refactorings/streamlining of pytest's own tests
--HG--
branch : trunk
(which can build C modules on the fly)
it's not clear they are still useful this way
and they are easy to confuse with pyimport()
--HG--
branch : trunk
hpk