Converting from tango.Atomic to D2 core.atomic

[dsimcha]

== Quote from eris (jvburnes at gmail.com)'s article
> a) core.atomic implements nearly all binary ops as well as nearly all
> assignment / increment ops.  But it doesn't implement the simplest of the ops:
> load, store.  Are these assumed to "just work" for ints and doubles?  If so,
> fine, but there are platform-dependent gotchas lurking along that path.

core.atomic does do atomic load/store as of 2.053.