BUG: _Openpyxl2Writer mishandles merged cell style
Thanks to @jtratner for catching this.

can u include a test for that inner loop (as clearly no test exists now)
 I'll see what I can do, perhaps tomorrow night.
 It's stunning how much time can pass in a blink before getting to "tomorrow night."
 @neirbowj this needs to go in 0.15.0, yes?
 merged via https://github.com/pydata/pandas/commit/e0d9b1a7807c41374b0212c3b09d5b73c1fecec6

thanks!
