First set of changes for reorganized cache coherence support.

First set of changes for reorganized cache coherence support.
Compiles but doesn't work... committing just so I can merge
(stupid bk!).

src/mem/bridge.cc:
    Get rid of SNOOP_COMMIT.
src/mem/bus.cc:
src/mem/packet.hh:
    Get rid of SNOOP_COMMIT & two-pass snoop.
    First bits of EXPRESS_SNOOP support.
src/mem/cache/base_cache.cc:
src/mem/cache/base_cache.hh:
src/mem/cache/cache.hh:
src/mem/cache/cache_impl.hh:
src/mem/cache/miss/blocking_buffer.cc:
src/mem/cache/miss/miss_queue.cc:
src/mem/cache/prefetch/base_prefetcher.cc:
    Big reorg of ports and port-related functions & events.
src/mem/cache/cache.cc:
src/mem/cache/cache_builder.cc:
src/mem/cache/coherence/SConscript:
    Get rid of UniCoherence object.

--HG--
extra : convert_revision : 7672434fa3115c9b1c94686f497e57e90413b7c3