merge revision(s) 48896: [Backport #10622]

	* ext/bigdecimal/depend: Fix dependencies to make bigdecimal
	  installable by rubygems.

	* ext/bigdecimal/bigdecimal.gemspec: version 1.2.6.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_2@48899 b2dd03c8-39d4-4d8f-98ff-823fe69b080e