Update to 2.15

* Use Lightning in seamonkey tar ball, 2.0pre.

Changelog:
SeaMonkey-specific changes

    SeaMonkey can be set as default client/browser on Mac and Linux now.
    See the changes page for minor changes.

Mozilla platform changes

    The new IonMonkey compiler improves JavaScript performance.
    Preliminary support for WebRTC has been added.
    Image quality has been improved through a new HTML scaling algorithm.
    CSS3 Flexbox has been implemented.
    Support for new DOM property window.devicePixelRatio has been added.
    Support for @supports has been added (disabled for now).
    Startup time has been improved through smart handling of signed extension certificates.
    HTML5: Support for W3C touch events has been implemented, taking the place of MozTouch events
    Insecure content loading has been disabled on HTTPS pages (see bug 62178).
    Responsiveness for users on proxies has been improved.
    Fixed several stability issues.

Fixed in SeaMonkey 2.15
MFSA 2013-20 Mis-issued TURKTRUST certificates
MFSA 2013-19 Use-after-free in Javascript Proxy objects
MFSA 2013-18 Use-after-free in Vibrate
MFSA 2013-17 Use-after-free in ListenerManager
MFSA 2013-16 Use-after-free in serializeToStream
MFSA 2013-15 Privilege escalation through plugin objects
MFSA 2013-14 Chrome Object Wrapper (COW) bypass through changing prototype
MFSA 2013-13 Memory corruption in XBL with XML bindings containing SVG
MFSA 2013-12 Buffer overflow in Javascript string concatenation
MFSA 2013-11 Address space layout leaked in XBL objects
MFSA 2013-10 Event manipulation in plugin handler to bypass same-origin policy
MFSA 2013-09 Compartment mismatch with quickstubs returned values
MFSA 2013-08 AutoWrapperChanger fails to keep objects alive during garbage collection
MFSA 2013-07 Crash due to handling of SSL on threads
MFSA 2013-06 Touch events are shared across iframes
MFSA 2013-05 Use-after-free when displaying table with many columns and column groups
MFSA 2013-04 URL spoofing in addressbar during page loads
MFSA 2013-03 Buffer Overflow in Canvas
MFSA 2013-02 Use-after-free and buffer overflow issues found using Address Sanitizer
MFSA 2013-01 Miscellaneous memory safety hazards (rv:18.0/ rv:10.0.12 / rv:17.0.2)

(ryoon)