Added a SIGINT handler that unmounts.
Added a SIGINT handler that unmounts.

Fixes #4.

mbrukman/gcsfuse,GoogleCloudPlatform/gcsfuse,BanzaiMan/gcsfuse,GoogleCloudPlatform/gcsfuse,BanzaiMan/gcsfuse,kahing/gcsfuse,jacobsa/ratelimit,GoogleCloudPlatform/gcsfuse,jacobsa/timeutil