PLT-426 - TimeSeriesRelativeWeightedDifferenceOperator does not handle weights of 0

Add code and test to handle weights of zero
PLT-426 - TimeSeriesRelativeWeightedDifferenceOperator does not handle weights of 0

Fix typo in method name
Merge pull request #195 from OpenGamma/topic/PLT-426

PLT-426 - TimeSeriesRelativeWeightedDifferenceOperator does not handle w...
[PLAT-6779] Simple utility to calculate the number of business days between two dates
[PLAT-6779] Added method to BusinessDayDateUtils
Merge pull request #196 from OpenGamma/topic/PLAT-6779

topic/PLAT-6779
Merge branch 'refs/heads/develop' into topic/REQS-526

Conflicts:
	projects/OG-Analytics/src/main/java/com/opengamma/financial/convention/daycount/BusinessTwoFiveTwo.java
[REQS-526] Variance Swap demo
[PLAT-6783] The method present value of VarianceSwapStaticReplication has a fencepost error
[PLAT-6779] Simple utility to calculate the number of business days between two dates
[PLAT-6785] Remove observation frequency from VarianceSwapDefinition and EquityVarianceSwapDefinition