[analyzer] Remove strip of ElementRegion in CallEvent::invalidateRegions.

This is a bit of old code trying to deal with the fact that functions that
take pointers often use them to access an entire array via pointer
arithmetic. However, RegionStore already conservatively assumes you can use
pointer arithmetic to access any part of a region.

Some day we may want to go back to handling this specifically for calls,
but we can do that in the future.

No functionality change.
[analyzer] Invalidate regions indirectly accessible through const pointers.

In this case, the value of 'x' may be changed after the call to indirectAccess:

  struct Wrapper {
    int *ptr;
  };

  void indirectAccess(const Wrapper &w);

  void test() {
    int x = 42;
    Wrapper w = { x };

    clang_analyzer_eval(x == 42); // TRUE
    indirectAccess(w);
    clang_analyzer_eval(x == 42); // UNKNOWN
  }

This is important for modelling return-by-value objects in C++, to show
that the contents of the struct are escaping in the return copy-constructor.

<rdar://problem/13239826>
[analyzer] Track malloc'd memory into struct fields.

Due to improper modelling of copy constructors (specifically, their
const reference arguments), we were producing spurious leak warnings
for allocated memory stored in structs. In order to silence this, we
decided to consider storing into a struct to be the same as escaping.
However, the previous commit has fixed this issue and we can now properly
distinguish leaked memory that happens to be in a struct from a buffer
that escapes within a struct wrapper.

Originally applied in r161511, reverted in r174468.
<rdar://problem/12945937>
[analyzer] Don't invalidate globals when there's no call involved.

This fixes some mistaken condition logic in RegionStore that caused
global variables to be invalidated when /any/ region was invalidated,
rather than only as part of opaque function calls. This was only
being used by CStringChecker, and so users will now see that strcpy()
and friends do not invalidate global variables.

Also, add a test case we don't handle properly: explicitly-assigned
global variables aren't being invalidated by opaque calls. This is
being tracked by <rdar://problem/13464044>.