(1) support Example functions defined in programs that don't
import "testing". We emit code to testmain.main() to call
them directly, since we can't call testing.Main.
(2) expose a FindTests function which reports the set of
Test, Example and Benchmark functions it finds.
Certain clients need this.
Added test for logic in FindTests.
LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/115290048
Alan Donovan