cmd/go: every test imports regexp
cmd/go: every test imports regexp

This fixes the bug Rob ran into when editing package bytes.
Regexp imports regexp/syntax, which imports bytes, and
regexp/syntax was not being properly recompiled during a
test of a change to package bytes.

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5555065

rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,webfd/go-zh,rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,webfd/go-zh,Triskite/willstone-goclone,rdp/rogerpack2005-golang,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,bryanxu/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,bryanxu/go-zh,bryanxu/go-zh,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,d0f/go-zh,Triskite/willstone-goclone,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,mhennings/marcohennings-go,d0f/go-zh,webfd/go-zh,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,scirelli/scirelli-go,webfd/go-zh,mhennings/marcohennings-go,Triskite/willstone-goclone,scirelli/scirelli-go,mhennings/marcohennings-go,d0f/go-zh,bryanxu/go-zh,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,webfd/go-zh,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,Triskite/willstone-goclone,bryanxu/go-zh,rdp/rogerpack2005-golang,Triskite/willstone-goclone,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,Triskite/willstone-goclone,mhennings/marcohennings-go,d0f/go-zh,webfd/go-zh,Triskite/willstone-goclone,rdp/rogerpack2005-golang,d0f/go-zh,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,scirelli/scirelli-go,webfd/go-zh,mhennings/marcohennings-go,bryanxu/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,sanjosh/sanjos100-tipc