[MERGE] Try harder to avoid loading plugins during the test suite.

[Ian Clatworthy]

Ian Clatworthy has voted approve.
Status is now: Approved
Comment:
Please check Vincent is happy before merging. Fine by me.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C20090108055547.GA26450%40steerpike.home.puzzling.org%3E
Project: Bazaar