run.files keys can collide if specified by relative URLs

[ghost]

If two files in the run.files dictionary have the same relative URL, but relative to different uriBaseIds, then they will collide (they will have the same key).

One option (suggested by @michaelcfanning) would be to allow the key to be constructed from uriBaseId + relative URL.

[ghost]

Accidentally closed the wrong issue.

[ghost]

The solution we came up with is to encode the uriBaseId in the property name if necessary to avoid a property name collision, for example:

"files": {
  "#SRCROOT#utilities.c": {
    ...
  },
  "#TESTSRCROOT#utilities.cs": {
    ...
  }
}