Ability to blacklist keywords; they will be replaced by valid alternatives.

A major problem porting GM games has to do with C++ keywords ("try") or even just global namespace garbage ("time") interfering with GM variable names. In many cases, there are hundreds of these variables to change in hard-to-reach places (like map initialization).

This adds a setting to the "Compatibility" panel called "keyword blacklist". Any variable (e.g., "test") in this comma-separated list will be replaced by, e.g., "test______".  By default this list is empty.

At the moment, this switch is done in syntacheck(), so it would, for example, be a bad idea to blacklist "var". I think this is sufficient for the V1 parser; the new parser can probably do a more intelligent variable-only replacement, if that is in fact needed.