Minimal test for regex (#1038)

This is useful for testing the build system becaues regex is a fairly
small package that uses C.

packages/regex/test_regex.py

@@ -0,0 +1,3 @@
+def test_regex(selenium, request):
+    selenium.load_package("regex")
+    assert selenium.run("import regex\nregex.search('o', 'foo').end()") == 2