New functionality for instcombine:

   * New ReplaceInstUsesWith function to factor out tons of common code
     This needs to be used more in the future still, but it's a good start
   * New InsertNewInstBefore to allow multi-instruction replacements
   * Change getMaxValue functions to isAllOnesValue function, which doesn't
     have to CREATE/lookup a new constant.  Also the name is accurate
   * Add new isMaxValue, isMinValue, isMaxValueMinusOne, isMinValuePlusOne
     functions:  This should be moved to Constant* classes eventually
   * Implement xor X, ALLONES -> not X
   * Fold ALL setcc's of booleans away
   * Handle various SetCC's for integers against values at the end of their
     ranges, possibly off by one.  This implements the setcc-strength-reduce.ll
     testcase.

llvm-svn: 3286