fix binaryFun

1. Make binaryFun correct for integer comparison.
2. Remove import of half of phobos for 98% cases in phobos.

`sort`, `cmp`, `find`, `startsWith`,  `sum` and other algorithms would be compiled faster.

See also: #2701, [Issue 13253 - use more scoped imports in phobos](https://issues.dlang.org/show_bug.cgi?id=13253)

Andrei talked about this before. If we can somehow get a hash of the AST tree of the lambda or something, we might be able to implement equality between lambdas. But I don't know enough dmd internals to be able to tell how feasible this is.