Add missing headers to bsl_memory.h

A couple of headers defining parts of the 'bsl' interface
were factored out of 'bslstl_sharedptr.h' during development,
and we forgot to add them to 'bsl_memory.h' to enusre that
they remained accessible to users.
Corrected metadata
[APPROVAL] review/missing_headers_in_bsl_memory_drqs59127285 to master
Fix bslstl::shared_ptr build in -std=c++11 due to typo.
[APPROVAL] bslstl-sharedptr-cpp11-fix-REBASED-drqs-58999996 to master