Redid the contents of ObjectProxy in preparation for requiring a source.
Redid the contents of ObjectProxy in preparation for requiring a source.

We might as well always have a source. The file inode creation code
assumes it, and we'll probably want to start by creating an empty object
and branching from that in Create. This is good -- it gives us atomic
create and open as fuse desires.

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