Tor should accept combined pluggable transport names

The plan for #7167 (moved) is to have flashproxy understand pluggable transporst like "websocket|obfs2", that is the combination of websocket and obfs2.

The good thing about our plan for #7167 (moved) is that it requires no real modifications to little-t-tor. However, in little-t-tor we do some checks on the transport names (in torrc, etc.) and ensure that they are C-identifiers -- but "websocket|obfs2" is not a C-identifier.

We should relax those checks so that they don't choke when we give them "websocket|obfs2".