proposed fix for #669

Only if we need test-1.2.3 for anything else than Rails2/CP.
(if not, just change Gemfile condition to "and chiliproject")

This reverts commit 0cd902610fb6a8d7fdc6c11c783d085cfb9adb32, and adds alternative solution.
Merge pull request #797 from inger/master

reworked fix for #669 (the infamous test-unit bundle conflict)
globally exporting IN_RBL_TESTENV=true fixes testing