views_var_export() doesn't properly encode array keys

This is valid in all versions of Views (6.x-2.x, 6.x-3.x, 7.x-3.x): views_var_export() doesn't properly encode array keys:

$output .= "  '$key' => " . views_var_export($value, '  ', FALSE) . ",\n";

Should be:

$output .= "  " . views_var_export($key, '  ', FALSE) . " => " . views_var_export($value, '  ', FALSE) . ",\n";

Critical because it means that Views exports are broken as soon as an array key contains a single quote.