race.bat: fix env setup

Currently it fails as:
go tool dist: $GOROOT is not set correctly or not exported
GOROOT=c:\go
c:\go\include\u.h does not exist
Fail.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/42550044

src/race.bat

@@ -15,6 +15,7 @@ echo race.bat must be run from go\src
 goto end
 :ok
 
+set GOROOT=%CD%\..
 call make.bat --dist-tool >NUL
 if errorlevel 1 goto fail
 .\cmd\dist\dist env -wp >env.bat
@@ -35,7 +36,7 @@ go install -race cmd/cgo
 echo # go install -race std
 go install -race std
 if errorlevel 1 goto fail
-echo # go test -race -short -std
+echo # go test -race -short std
 go test -race -short std
 if errorlevel 1 goto fail
 echo # go test -race -run=nothingplease -bench=.* -benchtime=.1s -cpu=4 std