Change deflate.go's default compression level from 4 to 6.
Change deflate.go's default compression level from 4 to 6.

R=rsc
APPROVED=rsc
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=35208
CL=35261
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go