Add missing option
Completely remove variables from spell checking

Variables with full names might otherwise still be subjected to spell
checking.
Add a more obvious spelling error

Depending on the spell checker, Mozilla might be in the English dictionary
so let's rather make it easier to test a real error.
Typo
Avoid unnecessary object creation
Limit the number of cases where we augment the term list.

More work needed here; see bug 3017.
Remove unused import
Provide a simpler, faster API

This function only returns errors, not their positions or suggestions.
Providing suggestions are very slow.
Rewrite spelling test

This uses the new, faster API for spelling and uses set operations
and caching for substantially better performance of this quality
check when editing long texts in Virtaal. The shorter error messages
might actually be a small usability improvement for Virtaal.