Ruby 1.9

[Jeremy Lavergne]

>   rb-rubygems @1.3.7_0+ruby (active)

So your gems are ruby are presumably 1.8.7 and your binary is ruby 1.9.3.

$ port variants rb-rubygems
rb-rubygems has the variants:
[+]ruby: add Ruby 1.8.7 support
     * conflicts with ruby186 ruby19
   ruby186: add Ruby 1.8.6 support
     * conflicts with ruby ruby19
   ruby19: add Ruby 1.9 support
     * conflicts with ruby ruby186

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