bzrlib.option should allow an option that allows argument starting with dash (-)

This came up as a bug #591233 against bzr-grep.

<lifeless> it will parse it as option 'b' with param 'lah' and no parameters given to 'e'
<parthm> lifeless: yes. thats what i got when i tried it.
<lifeless> Thats what I'd expect to happen; I don't think this is really a bug is it? just escape the - - -e "\\-blah"
<parthm> lifeless: yes. thats the workaround i suggested in the bug. but posix grep supports -e ... so i suppose people used to posix grep would try that first.
<parthm> so its not critical, but nice to have.
<lifeless> so, if you find a way to add this to bzr core
<lifeless> I'd like to suggest that it be made obvious in two places
<lifeless> the docstrings for any objects that will sometimes-handle-leading-dash-and-sometimes-not
<lifeless> and the help for commands that use such options - automatically in the this second case