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)

Ah, okay, now I see what you are referring to, the `reduce` call in the default implementation of `sum` with seed. However, in that case, it would be enough to make `sum` use a lambda, wouldn't it?