Rails3: test: replace deprecated Errors#on to Errors#[] and join with to_s at test/unit/time_entry_activity_test.rb
On Rails2, Errors#[] returns single error if one error raises. But, on Rails3, Errors#[] always returns the array.
Authored by: tmaruyama 2011-12-09
Parent: [r8135]
Child: [r8137]
