Provide a thin abstraction to locate the CForLoop that contains a given CForLoop header clause
Merge pull request #936 from noakesmichael/primBlock

Loop Invariant Code Motion currently encounters BlockStmts that represent the init/test/incr clauses of a
CForLoop and needs to be able to get a pointer to the enclosing CForLoop.  Provide a simple abstraction
so that the implementation can change whenever the internal representation of a CForLoop changes.

Compiled: STD clang/darwin, STD gcc/linux64, LLVM gcc/linux64
Tested: paratest --verify
Review: None