gob: eliminate two more allocations in decode. - just an oversight; we were reallocating a buffer. - use unsafe to avoid allocating storage for a string twice.
gob: eliminate two more allocations in decode.
- just an oversight; we were reallocating a buffer.
- use unsafe to avoid allocating storage for a string twice.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4290056

ssrl/go,ssrl/go,apparentlymart/golang,dsriram/golang,dsriram/golang,gnanderson/go,ssrl/go,pombredanne/go-deleteme,dsriram/golang,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,ssrl/go,dsriram/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,gnanderson/go,dsriram/golang,gnanderson/go,dsriram/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,ssrl/go,tv42/old-go,gnanderson/go,apparentlymart/golang,dsriram/golang,ssrl/go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,ssrl/go,gnanderson/go,tv42/old-go,tv42/old-go