Fix variable shadowing + other compiler warnings

[don-clugston-sociomantic]

There are a couple of instances of foreach variable shadowing, a missing return annotation, and some D1-style in operators which need D2 replacements.

After these changes, when my ocean fixes are merged, swarm unittests compile cleanly on dmd 2.092 beta, with the exception of the two 'escaping variable' issues which I created an issue about.