Slight fixes, add in commit trace flag.

Slight fixes, add in commit trace flag.

base/traceflags.py:
    Add new commit rate trace flag.
build/SConstruct:
    Add extra option for efence.
cpu/beta_cpu/alpha_full_cpu_impl.hh:
    Use function calls instead of direct indexing (avoids confusion).
cpu/beta_cpu/commit_impl.hh:
    Add commit rate trace output (might not be worthwhile in the future).
cpu/beta_cpu/decode_impl.hh:
    Remove some older hacks.  Fix it so that the isntruction properly sets its next
    PC to the one calculated by the branch.
cpu/beta_cpu/fetch_impl.hh:
    Remove old commented code.
cpu/beta_cpu/iew_impl.hh:
    Add extra check to ensure that the instruction is valid.
cpu/beta_cpu/regfile.hh:
    Include trace file.

--HG--
extra : convert_revision : 4ee1dc88f8a5ed9b65486c6c111a3718a8040e42