[analyzer; alternate edges] improve support for edges with PseudoObjectExprs.

This optimizes some spurious edges resulting from PseudoObjectExprs.
This required far more changes than I anticipated.  The current
ParentMap does not record any hierarchy information between
a PseudoObjectExpr and its *semantic* expressions that may be
wrapped in OpaqueValueExprs, which are the expressions actually
laid out in the CFG.  This means the arrow pruning logic could
not map from an expression to its containing PseudoObjectExprs.

To solve this, this patch adds a variant of ParentMap that
returns the "semantic" parentage of expressions (essentially
as they are viewed by the CFG).  This alternate ParentMap is then
used by the arrow reducing logic to identify edges into pseudo
object expressions, and then eliminate them.

llvm-svn: 182083