1. Fix a carry out problem in add if destination and x point to the same

1. Fix a carry out problem in add if destination and x point to the same
   memory (as done in fromString).
2. Implement Knuth divide more closely to what is recommended in his book.
3. Fix computation of the remainder for Knuth Divide (bad shifting).
4. Remove some cruft from the file

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34518 91177308-0d34-0410-b5e6-96231b3b80d8