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)

I'm not sure that documenting these is a good idea. The optimization is just an implementation detail, right? In that case, there is no need to bother the user with this, as it doesn't change any of the semantics.