Instiki 0.19.2

Bump version number.

Also update to a faster method
of loading MathJax (thanks to
Davide Cervone for assistance).

app/controllers/application_controller.rb

@@ -279,7 +279,7 @@ module Instiki
     MINOR = 19
     TINY  = 2 
     SUFFIX = '(MML+)'
-    PRERELEASE =  'pre'
+    PRERELEASE = false
     if PRERELEASE
        STRING = [MAJOR, MINOR].join('.') + PRERELEASE + SUFFIX
     else