CLEANUP: .gitignore: finally ignore everything but what is known.

Still too many files remain, it's easier to block everything but
what we know.

.gitignore

@@ -46,3 +46,23 @@ tests/test_hashes
 /*.sh
 /bug*
 /TAGS
+# Below we forbid everything and only allow what we know, that's much easier
+# than blocking about 500 different test files and bug report outputs.
+/.*
+/*
+!/.gitignore
+!/CHANGELOG
+!/LICENSE
+!/Makefile
+!/README
+!/ROADMAP
+!/SUBVERS
+!/VERDATE
+!/VERSION
+!/contrib
+!/doc
+!/ebtree
+!/examples
+!/include
+!/src
+!/tests