Fix it so that the cache does not assume to gave the packet it sent out via sendTiming.

Fix it so that the cache does not assume to gave the packet it sent out via sendTiming.
Still need to fix upgrades to use this path

src/mem/cache/base_cache.cc:
    Copy the pkt to the MSHR before issuing the sendTiming where it may be changed/consumed
src/mem/cache/cache_impl.hh:
    Use copy of packet, because sendTiming may have changed the pkt
    Also, delete the copy when the time comes

--HG--
extra : convert_revision : 635cde6b4f08d010affde310c46b1caf50fbe424