merge revision(s) r45393: [Backport #9668]

	* gc.c: Fix up default GC params by @csfrancis [fix GH-556]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@45810 b2dd03c8-39d4-4d8f-98ff-823fe69b080e