test: put GOROOT/bin before all others in run

If you installed a 6g in /usr/bin it interferes
with test/run otherwise.

R=rsc
CC=golang-dev
https://golang.org/cl/4944046

test/run

@@ -31,7 +31,7 @@ unset GREP_OPTIONS	# in case user has a non-standard set
 
 failed=0
 
-PATH=/bin:/usr/bin:/usr/local/bin:${GOBIN:-$GOROOT/bin}:`pwd`
+PATH=${GOBIN:-$GOROOT/bin}:`pwd`:/bin:/usr/bin:/usr/local/bin
 
 RUNFILE="/tmp/gorun-$$-$USER"
 TMP1FILE="/tmp/gotest1-$$-$USER"