Fixed WatchChanges not properly removing subdirectories from watch list

[daniel-chambers]

In the scenario where WatchChanges is used with multiple includes, if one include is a subdirectory of another, WatchChanges will not watch the correct directory.

For example:

use watcher = 
    !! "parent/*.*" ++ "parent/child/*.*"
    |> WatchChanges (fun changes ->
        tracefn "%A" changes)

/parent/child will be watched (incorrectly), instead of /parent.

This PR fixes this issue and refactors the code a little in order to implement a couple of tests to ensure the correct behaviour when eliminating subdirectories from the watch list.

[forki]

could you please look at the build error?

[daniel-chambers]

Damn, it seems like a failure when building on Mono because of paths in the tests. Do you guys have a way of automatically handling the difference between \ on Windows and / on *nix?

[forki]

there should be a normalizepath function somewhere in the repo. just call that

[daniel-chambers]

Fixed :)

I used an internal function from Globbing, which makes me a little uncomfortable, but it was the only one I found.