Log Message:
Update rcairo to 1.6.3.

Release 1.6.3 (2008-07-19) Kouhei Sutou <kou@cozmixng.org>)
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Features
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  * Fix build failure on Debian GNU/Linux. (reported by James Healy)
  * Fix GC failure with Ruby 1.8.7. (reported by James Healy)
  * Improve building on MacOS X. (suggested by Carsten Bormann)
  * Fix install location of cairo.so. (suggested by OBATA Akio)