Tweak behavior of submit buttons on register and login pages

The buttons are not re-enabled if the registration/login submission succeeds
(and, therefore, the user is about to be directed to another page). Also, any
error message that is present does not disappear immediately before the page
redirects.
Update MathJax to the latest stable version (2.2), to fix IE10 bug LMS-194
Merge pull request #406 from edx/gprice/register-button-enabling-tweak

Tweak behavior of submit buttons on register and login pages
Merge pull request #412 from edx/dave/ie10_mathjax_fix

Update MathJax to the latest stable version (2.2), to fix IE10 bug LMS-194
changed transifex project to edx-platform
Merge pull request #414 from edx/jtauber/switch-transifex-project

changed transifex project to edx-platform
Merge branch 'master' of github.com:edx/edx-platform into feature/kluo/bulk-email
Improve robustness for email optout ajax
Merge branch 'feature/kluo/bulk-email' of github.com:edx/edx-platform into feature/kluo/bulk-email