Tree marking is case-sensitive

[madakk]

The code looking up the currently open files assumes the paths are the same case as the path data in the tree, but that doesn't always seem to be the case. For example, in my case, the P4 workspace root was set to "c:" with a lowercase C, but in the tree the paths had an uppercase C, causing the marking to fail.

[madakk]

I guess this goes beyond marking, the code matching the current buffer with any open files suffers from the same problem.