Fix several bugs pertaining to upgrades/mem leaks.

Fix several bugs pertaining to upgrades/mem leaks.

src/mem/cache/base_cache.cc:
    Fix a bug about not having a request to send
src/mem/cache/base_cache.hh:
    Fix a bug with the blocking code
src/mem/cache/cache.hh:
    A\bFix a bug with snoop hits in WB buffer
src/mem/cache/cache_impl.hh:
    Fix a bug with snoop hits in WB buffer
    Also, add better DPRINTF's
src/mem/cache/miss/miss_queue.cc:
    Fix a bug with upgrades (Need to clean it up later)
src/mem/cache/miss/mshr.cc:
    Fix a memory leak bug, still some outstanding with writebacks not being deleted
src/mem/cache/miss/mshr_queue.cc:
    Fix a bug about upgrades (need to clean up later)
src/mem/packet.hh:
    Fix for newly added cmd attribute for upgrades
tests/configs/memtest.py:
    More interesting testcase

--HG--
extra : convert_revision : fcb4f17dd58b537bb4f67a8c835f50e455e8c688