[analyzer] Make sure a temporary object region matches its initial bindings.

When creating a temporary region (say, when a struct rvalue is used as
the base of a member expr), make sure we account for any derived-to-base
casts. We don't actually record these in the LazyCompoundVal that
represents the rvalue, but we need to make sure that the temporary region
we're creating (a) matches the bindings, and (b) matches its expression.

Most of the time this will do exactly the same thing as before, but it
fixes spurious "garbage value" warnings introduced in r175234 by the use
of lazy bindings to model trivial copy constructors.

<rdar://problem/13265460>
<rdar://problem/13265017>

The notion of Crossref command has long been forgotten, and there is nothing using CommandObjectCrossref in the current LLDB codebase
However, this was causing a conflict with process plugins and command aliases ending up in an infinite loop under situations such as:
(lldb) command alias monitor process plugin packet monitor
(lldb) process att -n Calendar
Process 28709 stopped
Executable module set to "/Applications/Calendar.app/Contents/MacOS/Calendar".
Architecture set to: x86_64-apple-macosx.
(lldb) command alias monitor process plugin packet monitor

This fixes the loop (and consequent crash) by disposing of Crossref commands and related code