Log Message:
Update rcairo to 1.7.0.

Release 1.7.0 (2008-08-16) Kouhei Sutou <kou@cozmixng.org>)
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Features
--------
  * Support cairo 1.7.4.
  * Add new methods:
    * Cairo::Context#destroy
    * Cairo::Surface#destroy
    * Cairo.satisfied_version?
  * Resupport ruby 1.9. (suggested by Paul van Tilburg)
  * Fix README. (suggested by Davide Rambaldi)