Per conversations with Zhongxing, add an 'element type' to

Per conversations with Zhongxing, add an 'element type' to
ElementRegion.  I also removed 'ElementRegion::getArrayRegion',
although we may need to add this back.

This breaks a few test cases with RegionStore:
- 'array-struct.c' triggers an infinite recursion in RegionStoreManager.  Need to investigate.
- misc-ps.m triggers a failure with RegionStoreManager as we now get the diagnostic:
  'Line 159: Uninitialized or undefined return value returned to caller.'

There were a bunch of places that needed to be edit
RegionStoreManager, and we may not be passing all the correct 'element
types' down from GRExprEngine.

Zhongxing: When you get a chance, could you review this?  I could have
easily screwed up something basic in RegionStoreManager.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70830 91177308-0d34-0410-b5e6-96231b3b80d8