Update to 2.13

* Update enigmail to 1.4.5
* Update Mozilla Lightning to 1.8

Changelog:
SeaMonkey-specific changes

    None.

Mozilla platform changes

    JavaScript responsiveness has been improved through incremental garbage collection.
    CSS3 Animations, Transitions, Transforms and Gradients have been unprefixed.
    MD5 is no longer supported as a hash algorithm in digital signatures.
    The Opus codec is now support by default.
    The reverse CSS3 animation direction has been implemented.
    Per tab reporting is now available in about:memory.
    Fixed several stability issues.

(ryoon)