Transform for loops over pseudo-arrays only if begin/end members exist

For loops using pseudo-arrays, classes that can be used like arrays from
the Loop Convert Transform's point of view, should only get transformed
if the pseudo-array class has begin()/end() members for the
range-based for-loop to call.

Free versions of begin()/end() should also be allowed but this is an
enhancement for another revision.

llvm-svn: 181539