TCP probes can now contain an optional path.

When a path is specified, instead of just trying to connect to specified
port, pingr will connect, then read whatever is sent by the server, until
either it finds the specified path (e.g. a login prompt), or it reaches a
timeout (which is still considered as a failure).
Merge pull request #1 from jpetazzo/master

TCP probes can now contain an optional path.