[Fix #1243] Fix multiline-block cop which errors out on empty blocks

Currently, the multiline block cop errors out when it encounters code like this
```
x do
end
```
This commit checks for such blocks, and handles the condition correctly.
Merge pull request #1244 from vrthra/fix/1243/multiline-block-empty

[Fix #1243] Fix multiline-block cop which errors out on empty blocks
Fix problem with Psych::ENGINE for ruby-head
Merge pull request #1248 from jonas054/fix_yaml_engine_problem

Fix problem with Psych::ENGINE for ruby-head
Make tests run and pass in random orders

Running tests in random order exposes potential dependencies to stale data.

* Clear out some class-level variables that cache values from previous tests
* Don't mutate the configuration object in tests:
  * Mutating the global config object affects other tests. Tests should be able
    to be run in random order. This fixes errors that surfaced when running in
    random order.
Merge pull request #1250 from gylaz/random-order-tests

Make tests run and pass in random orders
TrailingComma cop does auto-correction

Fix #1241
Merge pull request #1252 from yous/patch-trailing-comma-autocorrect

TrailingComma cop does auto-correction
[Fix #1254] Update parser to 2.2.0.pre.4
Ignore block-pass in `TrailingComma`

Trailing commas after a block-pass are a parse error, so we must
special-case them.
Merge pull request #1256 from tamird/trailing-commas-block

Ignore block-pass in `TrailingComma`