test-help: improve test coverage
Adds a test for using the help option with the version option.
Extends test coverage of commands.help_ by another 2 lines.
adding foo
% no signatures
% hg sign 0
Signing 0:e63c23eaa88a
% hg sigs
hgtest 0:e63c23eaa88ae77967edcf4ea194d31167c478b0
% hg sigcheck 0
e63c23eaa88a is signed by:
hgtest