Fix an error in formatting of for-loops.

Two minor changes:
* Slight penalty for breaking at "," as opposed to ";".
* Don't apply bin-packing rules to for-loops.

Before:
for (int aaaaaa = aaaaaaaaaa; aaaaaa < bbbbbbbb; ++aaaaaa,
         ++ccccccccccccccc) {}

After:
for (int aaaaaa = aaaaaaaaaa; aaaaaa < bbbbbbbb;
     ++aaaaaa, ++ccccccccccccccc) {}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174308 91177308-0d34-0410-b5e6-96231b3b80d8