Use mod_rewrite instead of error handlers to redirect to cgimap

Using rewrites is a simpler method then relying on 404 errors and redirecting
Accept empty responses in tests

cgimap and the rails port return an empty response for some error
replies (e.g. 404 and 410). Make the test framework accept this.

If a test is expecting content, the nature of the content is tested
in the checks.

Fixes issues introduced in zerebubuth/openstreetmap-cgimap#26
Merge pull request #21 from pnorman/lighttpd_rewrite

Use mod_rewrite instead of error handlers to redirect to cgimap
Merge pull request #29 from pnorman/empty_error_test

Accept empty responses in tests