Several fixes:

Several fixes:
(1) Applied patch from Casey to implement iterator::operator= correctly:
    it should use a pointer, not a reference.
(2) Added operators == and !=, and method all().
(3) Important bug fix: excess bits need to be ignored in operations
    like ==, count(), and all().  We do this by ensuring excess bits
    in the last bitset are always 0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4837 91177308-0d34-0410-b5e6-96231b3b80d8