Taught s:Path.getParent to handle Windows paths.

There was an error in the function which prevented Windows paths
from being properly decoded.  This error was causing the ".. (up a dir)"
feature to fail due to an unhandled Invalid Argument exception.

Signed-off-by: Tim Henigan <tim.henigan@gmail.com>

plugin/NERD_tree.vim

@@ -2009,7 +2009,12 @@ endfunction
 "Return:
 "a new Path object
 function! s:Path.getParent()
-    let path = '/'. join(self.pathSegments[0:-2], '/')
+    if s:running_windows
+        let path = self.drive . '\' . join(self.pathSegments[0:-2], '\')
+    else
+        let path = '/'. join(self.pathSegments[0:-2], '/')
+    endif
+
     return s:Path.New(path)
 endfunction
 "FUNCTION: Path.getLastPathComponent(dirSlash) {{{3