Fixed ConfigFileBackend to create parent directory for storage

Ignore-this: ccd5c6c5b1efdf2350973548b0eecc34

darcs-hash:20090320095048-1e3d8-eabba63f946a5c5c1927069625fdad918906cc7e
make GreenInvitation methods coherent with Invitation's

- rename invite -> send_invite, accept -> accept_invite, end -> disconnect

darcs-hash:20090320101159-b2873-d17e4613efde18410b8935cc2e640f66179e8491