Added (in my branch only) support for P4HOST setting to p4bridge and p4api.net
Without this, I was unable to attach to a Perforce depot on assembla (which controls access through P4HOST somehow). p4bridge sends a help command at startup to determine what charset the server is using. When attaching to the assembla server this command failed without P4HOST being set, which caused the connection to fail. I modified the startup sequence to use P4HOST if it has been specified.