Apply hack by 'unphased' to fix mouse wheel up events for vim (and others?)

See this discussion on gmane: http://comments.gmane.org/gmane.comp.terminal-emulators.tmux.user/5498

Original patch to putty-X: https://github.com/atsepkov/putty-X/commit/bbcedf5a85ca1ccaa27005e7f7ebeb4c8a783b88