'grail' fixes for MIPS:

This isn't a good result.  It merely disables the new functionality on MIPS
because enabling it causes segfaults, even with --tool=none, the cause of
which are not obvious.  It is only chasing through conditional branches that
is disabled, though.  Chasing through unconditional branches (jumps and calls
to known destinations) is still enabled.

* guest_generic_bb_to_IR.c bb_to_IR(): Disable, hopefully temporarily, the key
  &&-recovery transformation on MIPS.

* VEX/priv/host_mips_isel.c iselWordExpr_R_wrk(), iselCondCode_wrk():

  - add support for Iop_And1, Iop_Or1, and IRConst_U1.  This code is my best
    guess about what is correct, but is #if 0'd for now.

  - Properly guard some Iex_Binop cases that lacked a leading check that the
    expression actually was a Binop.