Log Message:
Update thunderbird and thunderbird-gtk1 to 2.0.0.21.

Security fixes in this version:

MFSA 2009-10 Upgrade PNG library to fix memory safety hazards
MFSA 2009-09 XML data theft via RDFXMLDataSource and cross-domain redirect
MFSA 2009-07 Crashes with evidence of memory corruption (rv:1.9.0.7)

For more info, see http://www.mozilla.com/en-US/thunderbird/2.0.0.21/releasenotes/