restrict compile check options

allowed options are validate/error/silent

validate = only run chktex, exit status 0
error = run compilation, exit(1) if chktex fails
silent = run chktex, but always do full compilation

services/web/app/coffee/Features/Compile/CompileController.coffee

@@ -29,8 +29,8 @@ module.exports = CompileController =
 				options.compiler = req.body.compiler
 			if req.body?.draft
 				options.draft = req.body.draft
-			if req.body?.check
-				options.check = if req.body.check is "validate" then "validate" else undefined
+			if req.body?.check in ['validate', 'error', 'silent']
+				options.check = req.body.check
 			logger.log {options:options, project_id:project_id, user_id:user_id}, "got compile request"
 			CompileManager.compile project_id, user_id, options, (error, status, outputFiles, clsiServerId, limits, validationProblems) ->
 				return next(error) if error?