added JsStrip unit test files

This patch adds unit test files from the new release of JsStrip [1]. Some of the tests
currently fail pointing to bugs which are fixed in the new JsStrip release. The fixes
need to be ported to DokuWiki's js_compress function.

This patch also adds a way to output additional info when a test fails. It misuses
SimpleTest's signalling which is probably a bad idea but works for now.

http://code.google.com/p/jsstrip/

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