Reduce code bloat from assert!()

Assertions without a message get a generated message that consists of a
prefix plus the stringified expression that is being asserted. That
prefix is currently a unique string, while a static string would be
sufficient and needs less code.
Revert atomicrmw {max, min, umax, umin}
auto merge of #8150 : dotdash/rust/assert_bloat, r=huonw

Assertions without a message get a generated message that consists of a
prefix plus the stringified expression that is being asserted. That
prefix is currently a unique string, while a static string would be
sufficient and needs less code.
auto merge of #8151 : sanxiyn/rust/atomicrmw, r=cmr

#8039 broke ARM build, and nothing uses these yet.
register snapshots.
auto merge of #8177 : graydon/rust/2013-07-31-register-new-snapshots, r=thestinger

r? someone