Recognize Windows absolute urls. C:\, e:/, etc

Running curl during development cycle on a windows pc, can cause an annoying crash, if you try to load a curl module. toUrl function will return an invalid localDirectory/localDirectory/file, since it is unable to understand that a path that starts with C:\ or something like that is an absolute url. This improves the isAbsUrl function by updating the absUrl regex to include windows style absolute urls.
Does it make sense to only match on strings that *start with* C:\ (and the like)?

```js
absUrlRx = /^\/|^[^:]+:\/\/|^[A-Za-z]:[\\/]/,
```

(Note the caret (^) before the [A-Za-z] group.)