function findBrush(alias, showAlert)
{
  var brushes = sh.vars.discoveredBrushes,
    result = null
    ;

  if (brushes == null)
  {
    brushes = {};

    // Find all brushes
    for (var brushName in sh.brushes)
    {
      var brush = sh.brushes[brushName],
        aliases = brush.aliases
        ;

      if (aliases == null) {
        continue;
      }

      brush.className = brush.className || brush.aliases[0];
      brush.brushName = brush.className || brushName.toLowerCase();

      for (var i = 0, l = aliases.length; i < l; i++) {
        brushes[aliases[i]] = brushName;
      }
    }

    sh.vars.discoveredBrushes = brushes;
  }

  result = sh.brushes[brushes[alias]];

  if (result == null && showAlert)
    alert(sh.config.strings.noBrush + alias);

  return result;
}
Finds a brush by its alias.

@param {String} alias    Brush alias.
@param {Boolean} showAlert Suppresses the alert if false.
@return {Brush}        Returns bursh constructor if found, null otherwise.