fix an exception in gpg.py with multiples sigs for the same cset
- silly error, do not overwrite the variable we use for iterating
- correct 'hg help sign'
transaction abort!
rollback completed
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
abort: No such file or directory: .../test/bar