definitions of Numeric.

	* lib/rational.rb (to_i): should returns truncated self.

	* lib/complex.rb (numerator): requires
	  Integer#{numerator,denominator}.

	* lib/complex.rb (quo): do not use definition of Numeric.

	* lib/complex.rb (div, divmod, floor, ceil, truncate, round):
	  undef'ed.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@15489 b2dd03c8-39d4-4d8f-98ff-823fe69b080e