empowered implied vol methods for displaced diffusion
better handling of evaluation dates which are not business dates
Give names to intermediate results.

Bytes on the stack are cheap these days, so it's not necessary
to reuse data members at the expense of clarity.
fixed BlackCapFloorEngine bug: displacement parameter was lost
Merge pull request 124.
solved merge conflict
Merge branch 'master' of https://github.com/fametrano/quantlib
Removed xll version