the request to be reused, thus reducing garbage generation. 

Speed-up of ~35%.  Go-FUSE is now only 10% slower than libfuse.

Drop fuse.Attr return from Create, Mkdir, Mknod, Symlink, Link return.

This saves one alloc per request.

Dropping inodes is expensive (it looks through the entire tree), while
opendir/readdir/releasedir should be cheap.

call.

Fix bug in MemNodeFs.

This lowers memory pressure on concurrent loads of a filesystem that
has external latency (eg. network roundtrips).