* 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/trunk@48896 b2dd03c8-39d4-4d8f-98ff-823fe69b080e