parse.y: keyword argument without paren

* parse.y (IS_LABEL_POSSIBLE): allow labels for keyword arguments just
  after method definition without a parenthesis.  [ruby-core:52820]
  [Bug #7942]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39504 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_keyword.rb: suppress warning

* test/ruby/test_keyword.rb (TestKeywordArguments#m1): suppress
  argument prefix warning.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39505 b2dd03c8-39d4-4d8f-98ff-823fe69b080e