Introduce mInitClause, mTestClause, mIncrClause and remove cforInfoGet()
CForLoop: Update loopForClause() for the new internal representation
Merge pull request #972 from noakesmichael/cforLoop-2

CForLoop: Introduce instance variables for header state and deprecate use of BlockStmt::blockInfo

This is the final step in separating the primary While/For loop nodes from a reliance on BlockStmt:blockInfo

Compiled: STD clang/darwin, STD gcc/linux64
Tested: paratest --verify
Review: none