qt: Use GUIUtil::HtmlEscape to escape HTML

This is why we created this function. Avoids some #ifdef.
Merge pull request #2955 from laanwj/2013_08_htmlescape

qt: Use GUIUtil::HtmlEscape to escape HTML
fix help prompt
Merge pull request #2957 from Rav3nPL/patch-1

fix help prompt
fix the typo fix in linearize.py
Merge pull request #2959 from jmcorgan/fix-typo

fix the typo fix in linearize.py