the request to be reused, thus reducing garbage generation.
    
Back to old speed (10% slower than libfuse).

Add test for memory pressure. This brings performance back to 50%
slower than libfuse, but simplifies structure for future performance
improvements.

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.