std/bslhdrs - declare only relevant names

Components in 'bsl+bslhdrs' and 'bsl+stdhdrs' have bent to the will of
backwards compatibility and declared names that do not exist in the underlying
standard C++ headers.  This causes issues in strictly standard-compliant
headers since name declarations may clash or may not be found.

This commit only declares the appropriate names, preserving the old behavior
if the 'BSL_BLOOMBERG_LEGACY_CODE' define is present (which it should be in
legacy Bloomberg code going forward).  We can choose an alternate policy if we
so choose
Fix building with 'xcode 5'

In particular, include <sys/time.h> instead of <time.h> to get
platform-specific types related to time (making Darwin more like FreeBSD and
AIX).