This CL copies rsc.io/toolstash verbatim at commit
7508e1dd47d11b2fc45f544415e014e4f25d3f95
to golang.org/x/tools/cmd/toolstash.
There are no code changes to adapt it
to its new home; those will happen in a follow-up CL.
rsc.io/toolstash will be updated to contain only
a README and a doc.go redirecting readers.
Change-Id: Icbef4d72215a8b124f857587905b45902d6cdece
Reviewed-on: https://go-review.googlesource.com/32681
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
