load extensions only after the ui object has been completely initialized
This fixes a traceback printed when hg tries to print another traceback
after an extension fails to be loaded. Add a test for that.
abort: impossible time zone offset: 4444444
transaction abort!
rollback completed
abort: invalid date: '1\t15.1'
transaction abort!
rollback completed
abort: invalid date: 'foo bar'
transaction abort!
rollback completed
abort: invalid date: ' 1 4444'
transaction abort!
rollback completed
abort: date exceeds 32 bits: 111111111111
transaction abort!
rollback completed
abort: No such file or directory: .../test/bar