Fix undefined behavior in container swap tests.

These swap tests were swapping non-POCS non-equal allocators which
is undefined behavior. This patch changes the tests to use allocators
which compare equal. In order to test that the allocators were not
swapped I added an "id" field to test_allocator which does not
participate in equality but does propagate across copies/swaps.

This patch is based off of D26623 which was submitted by STL.

llvm-svn: 289358