run-tests.py: pass --install-scripts to setup.py
This avoids possible problems when the user has a ~/.pydistutils.cfg.
Fixes issue638. Patch provided by Ralf Schmitt.
*** failed to import extension badext: bit bucket overflowextension 'hgext.gpg' overrides commands: sigs sigcheck signhg help [COMMAND]show help for a command, extension, or list of commands