Added build option to treat exit != 0 as error

This is a compromize of the previous solution with past behavior.  The
key issue is that, when a build of Go code fails, the error is not
immediately obvious in the console output.  This adds an
"expectExitZero" option to build actions which, when set to true, causes
LiteBuild to treat a non-zero exit as an error.  It is currently only
enabled for "go build" and "go install" actions.  Consequently, failed
builds appear in red.
Auto-complete ignores strings and comments

This was implemented using the spell-checking system already in place in
the Kate files.  The idea is that if a region has spell-check enabled
(e.g. comments and strings) then it is written in a natural language,
and thus it is not code.

This also has the positive side effect of not including words found in
strings in regions that ARE auto-completed.