merge revision(s) 44374,44375,44376: [Backport #9290]
* README.EXT: add a document about RGenGC. Reviewed by havenwood. [misc #8962] * README.EXT.ja: ditto. * README.EXT: add a refer to URL.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@44397 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) 44374,44375,44376: [Backport #9290]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@44397 b2dd03c8-39d4-4d8f-98ff-823fe69b080e