test: Make run.go's errorcheck behave like testlib.
test: Make run.go's errorcheck behave like testlib.

testlib will complain about any unmatched errors left in errorchecks while run.go will not.

Fixes issue 4141.

R=golang-dev, minux.ma, remyoudompheng, rsc
CC=golang-dev
http://codereview.appspot.com/6614060

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