Fix remote file paths on Windows

Deployment is broken on Windows, because of the changes introduced
in ceede908f5bbeaf53fb729ee2e3d1ae32d9c46ca. On Windows,
path.normalize() produces file URIs with backslash separators (i.e.
"path1\path2\file.fl"), whereas the FTP spec requires to use forward
slashes as directory separators.

  * Add _constructRemotePath method that replaces all occurrences of
  backslashes to forward slashes in a given string.
  * Call _constructRemotePath upon file upload and revision file check.