merge revision(s) 44469: [Backport #9329]

	* lib/mkmf.rb (RbConfig): expand RUBY_SO_NAME for extensions
	  backward compatibility.  [ruby-core:59426] [Bug #9329]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@45082 b2dd03c8-39d4-4d8f-98ff-823fe69b080e