Ref #42.  On galeraparameters.rst, added an entry on the legend to indicate user unserviceable parameters, that is parameters that are strictly for troubleshooting purposes, not for production.  For each such parameters, added a superscript T for troubleshooting.  In the description for each entry, strengthened the language to further stress this point.
Merge branch '3.x' of https://github.com/codership/galera into 3.x