add --config global option. allows to set hgrc option on command line.
syntax: --config section.name=value
also add new test-globalopts to test all global options in one place.
adding aadding baNONEXISTENT: No such file or directoryaba: No such file or directoryNONEXISTENT: No such file or directorybaNONEXISTENT: No such file in rev 14467d15ef43ab