Override dialyzer flags

Override the dialyzer flags so that:

* There are no warnings about unmatched returns. Almost all Riak code is
  written to NOT explicitly match return values which are not used.
  Enabling this flag adds many warning messages that didn't exist before
  and I'm not ready to modify all the code just to make them go away.
  This requires a group discussion about code style in the Riak
  codebase.

* Don't warn on non-local returns. I think that Yokozuna code would be
  better if it didn't have any non-local returns but for now it does and
  I'm re-enabling this to be consistent with previous dialyzer target.
  Please enter the commit message for your changes. Lines starting