Introduce transitional CForLoop::loopHeaderSet(init, test, incr)
Convert a use of blockInfoSet on CForLoop in to the transitional assignment
Move the blockTag assignment in to loopHeaderSet
Merge pull request #899 from noakesmichael/lower-0

Provide a transitional API for CForLoop and utilize in lowerIterators

Compiled: STD clang/darwin, STD gcc/linux64, LLVM gcc/linux64
Tested: paratest --verify
Review: None