This MozillaThunderbird update fixes several security and non security
issues:

Changes in MozillaThunderbird:
- update to Thunderbird 31.3.0 (bnc#908009)
* MFSA 2014-83/CVE-2014-1587
Miscellaneous memory safety hazards
* MFSA 2014-85/CVE-2014-1590 (bmo#1087633)
XMLHttpRequest crashes with some input streams
* MFSA 2014-87/CVE-2014-1592 (bmo#1088635)
Use-after-free during HTML5 parsing
* MFSA 2014-88/CVE-2014-1593 (bmo#1085175)
Buffer overflow while parsing media content
* MFSA 2014-89/CVE-2014-1594 (bmo#1074280)
Bad casting from the BasicThebesLayer to BasicContainerLayer

- fix bashism in mozilla.sh script

- Limit RAM usage during link for ARM

- remove add-plugins.sh and use /usr/share/myspell directly
(bnc#900639)