This is a fix for #83 support @Rule on methods

[matthewfarwell]

Extend rules to support @rule public MethodRule someRule() { return new SomeRule(); }

Scala does not allow the creation of public fields. If you declare a field public, the field is created as private but with accessor methods.
To allow the use of @rule with Scala fields, this patch allows the addition
of @rule to methods. When BlockJUnit4ClassRunner retrieves the list of fields
that have the @rule annotation, it also searches for methods with @rule.
These methods are called and the values returned are added to the list of
TestRule.

@ClassRule has been similarly changed.

This is intended to be used as follows:

private ExpectedException thrown = rules.ExpectedException.none();

@rule public ExpectedException getThrown() {
return thrown;
}

or

@rule public Timeout getTimeout() {
return new Timeout(20);
}

The validation is exactly the same as for the fields, i.e the methods must be
public and return a TestRule/MethodRule. In the case of @ClassRule, the
methods must also be static.

[matthewfarwell]

This is a merged commit with the changes from https://github.com/KentBeck/junit/pull/306. I've created the new pull request because I was having problems with the git rebase, but the changes are the same. I'll close the other one when it's no longer necessary.

This is merged into master.