hgignore: ignoring misc/cgo/testso/main instead of /misc/cgo/testso/testso

test.bash does not remove main if the test fails, so it is good to keep main in .hgignore.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5784057

.hgignore

@@ -27,7 +27,7 @@ doc/tmpltohtml
 doc/articles/wiki/*.bin
 misc/cgo/life/run.out
 misc/cgo/stdio/run.out
-misc/cgo/testso/testso
+misc/cgo/testso/main
 misc/dashboard/builder/builder
 misc/goplay/goplay
 misc/osx/*.pkg