Clean warnings in tests

[aycabta]

Clean warnings below:

/path/to/rdoc/test/test_rdoc_parser_ruby.rb:786: warning: ambiguous first argument; put parentheses or a space even after `/' operator
/path/to/rdoc/test/test_rdoc_parser_ruby.rb:781: warning: assigned but unused variable - out
/path/to/rdoc/test/test_rdoc_parser_ruby.rb:1382: warning: assigned but unused variable - constant
/path/to/rdoc/test/test_rdoc_parser_ruby.rb:1383: warning: assigned but unused variable - constant2
/path/to/rdoc/test/test_rdoc_parser_ruby.rb:3642: warning: assigned but unused variable - const_d