testing: do not print 'no tests' when there are examples
testing: do not print 'no tests' when there are examples

I am not sure why RunTests and RunExamples are
exported, but I assume that because they are we
should not change the signature, so I added an
unexported global shared by Main and RunTests.

Fixes issue 3237.

R=golang-dev, gri
CC=golang-dev
http://codereview.appspot.com/5779043
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go