Changed the sorting code for CMaildirs.

  After profiling getting the paths and running transform(tolower)
 on them is slower than just using strcasecmp - and the latter has
 the same result.

  This is an optimization.
  TODO: Remove the padding on flags.

  has_flag() is an optimization blackspot.  It needs to be updated
 and the padding loop is probably a contributor to the slowness.