cmd/api: add exception file
Fixes build.

R=golang-dev, adg, bradfitz, dsymonds, dave
CC=golang-dev
https://golang.org/cl/6586074
diff --git a/src/run.bash b/src/run.bash
index f379ff5..1859555 100755
--- a/src/run.bash
+++ b/src/run.bash
@@ -112,7 +112,7 @@
 
 echo
 echo '# Checking API compatibility.'
-go tool api -c $GOROOT/api/go1.txt -next $GOROOT/api/next.txt
+go tool api -c $GOROOT/api/go1.txt -next $GOROOT/api/next.txt -except $GOROOT/api/except.txt
 
 echo
 echo ALL TESTS PASSED