fix(urlUtils): made removal of windows drive from path safer

Prior to this fix, the urlResolve method would automatically
strip the first segment of a path if the segment ends in a colon.
This was to correct undesired behavior in the $location service
using the file protocol on windows in multiple browsers (see #4680).

However, there could be cases where users intentionally 
have first path segments that end in a colon 
(although this conflicts with section 3.3 of rfc3986).

The solution to this problem is an extra check to make sure
the first path segment of the input url does not end with a colon,
to make sure we're only removing undesired path segments.

Fixes #4939
Merge branch 'master' of https://github.com/angular/angular.js
componentizd!