clang-format: Break before/between array subscript expressions.

clang-format used to treat array subscript expressions much like
function call (just replacing () with []). However, this is not really
appropriate especially for expressions with multiple subscripts.

Although it might seem counter-intuitive, the most consistent solution
seems to be to always (if necessary) break before a square bracket,
never after it. Also, multiple subscripts of the same expression should
be aligned if they are on subsequent lines.

Before:
  aaaaaaaaaaaaaaaaaaaaaaaaa[aaaaaaaaaaaaaaaaaaaaaaaaa][
      bbbbbbbbbbbbbbbbbbbbbbbbb] = c;
  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[
      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa][
      bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = ccccccccccc;

After:
  aaaaaaaaaaaaaaaaaaaaaaaaa[aaaaaaaaaaaaaaaaaaaaaaaaa]
                           [bbbbbbbbbbbbbbbbbbbbbbbbb] = c;
  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
      [aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa]
      [bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = ccccccccccc;

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@186153 91177308-0d34-0410-b5e6-96231b3b80d8
clang-format: Fix string literal breaking.

Before this patch, it did not cooperate with
Style::AlwaysBreakBeforeMultilineStrings. Thus, it would turn

  aaaaaaaaaaaa(aaaaaaaaaaaaa, "aaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaa");

into:

  aaaaaaaaaaaa(aaaaaaaaaaaaa, "aaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaa "
                              "aaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaa");

and only a second format step would lead to the desired (with that
option):

  aaaaaaaaaaaa(aaaaaaaaaaaaa,
               "aaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaa "
               "aaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaa");

This could even lead to clang-format breaking the string at a different
character and thus leading to a completely different end result.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@186154 91177308-0d34-0410-b5e6-96231b3b80d8