merge revision(s) r45187,r45205,r45212,r45213: [Backport #9570]

	* numeric.c (ruby_num_interval_step_size): check signs and get rid
	  of implementation dependent behavior of negative division.
	  [ruby-core:61106] [Bug #9570]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@45250 b2dd03c8-39d4-4d8f-98ff-823fe69b080e