cmCTestP4: Fix use of size_t

Use plain size_t, not std::size_t, for portability to older compilers
like VS 6.  Use iterators and reverse iterators instead of integer
indices to walk through std::vector<>s to avoid using size_t => int
conversion.
Merge topic 'ctest-p4' into next

b6fbd68 cmCTestP4: Fix use of size_t