Add document fails in Rainbow when root path uses '/'

[Former user]

Original [issue 43](https://code.google.com/p/okapi/issues/detail?id=43) created by @ysavourel on 2009-04-04T11:26:09.000Z:

In Windows, when the root path uses '/' (after save) for a custom root, you cannot add new document because the paths do not match anymore.

[Former user]

Comment [1.](https://code.google.com/p/okapi/issues/detail?id=43#c1) originally posted by @ysavourel on 2009-04-04T11:53:09.000Z:

Fixed by replacing '/' by platform-specific file separator when loading project file.