[PLAT-4949] Support clone-free InMemoryMasters

Although by default InMemoryMasters, when production hardened, clone
results before sending them back as part of a search, there are situations
where client code can guarantee that this isn't necessary.

This then avoids unnecessary CPU time and heap churn.

Conflicts:
	projects/OG-Component/src/main/java/com/opengamma/component/factory/master/InMemoryPortfolioMasterComponentFactory.java
	projects/OG-Component/src/main/java/com/opengamma/component/factory/master/InMemoryPositionMasterComponentFactory.java
	projects/OG-Master/src/main/java/com/opengamma/master/portfolio/impl/InMemoryPortfolioMaster.java
Merge branch 'dev/v2.1.x' of github.com:OpenGamma/OG-Platform into dev/v2.1.x