Improve line breaking in binary expressions.

If the LHS of a binary expression is broken, clang-format should also
break after the operator as otherwise:
- The RHS can be easy to miss
- It can look as if clang-format doesn't understand operator precedence

Before:
bool aaaaaaaaaaaaaaaaaaaaa = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa !=
                                 bbbbbbbbbbbbbbbbbb && ccccccccc == ddddddddddd;
After:
bool aaaaaaaaaaaaaaaaaaaaa =
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa != bbbbbbbbbbbbbbbbbb &&
    ccccccccc == ddddddddddd;

As an additional note, clang-format would also be ok with the following
formatting, it just has a higher penalty (IMO correctly so).
bool aaaaaaaaaaaaaaaaaaaaa = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa !=
                                 bbbbbbbbbbbbbbbbbb &&
                             ccccccccc == ddddddddddd;

llvm-svn: 181430