add SVI interpolation
Merge branch 'svi'

Conflicts:
	QuantLib/ql/experimental/volatility/Makefile.am
fix comparisons betwenn signed and unsigned integers
Merge branch 'fixSignCompNoarbSabr'
remove type specifiers from std::make_pair to make it c++11 compliant
Merge branch 'fixMakePairRDFMdl'