Backport Markov functional model fixes from master.

- Remove cap for F (this causes violations of the C^1 property in
  certain cases). Require decreasing call prices for exponential
  extrapolation.
- Fix floor pricing.
- Fix error check in vanilla engine tests, exclude 0.10 strike and
  change strike 0.07 to 0.06 in cap engine test, use correct yield
  and volatility termstructure in cap engine test.