-function makeLinter(name, filetype, cmd, args, errorformat, os, whitelist, domatch, loffset, coffset)
+-- callback: function to call before executing the linter, if it returns
+-- false the lint is canceled. The callback is passed the buf.
+-- optional param, default: nil
+function makeLinter(name, filetype, cmd, args, errorformat, os, whitelist, domatch, loffset, coffset, callback)