ATSUI support on Carbon Emacs

[YAMAMOTO Mitsuharu]

At the request of the maintainer, I installed ATSUI support on Carbon
Emacs to the trunk.  It does not change anything unless -DUSE_ATSUI is
specified at compile time.  It is still somewhat experimental, and has
some known problems:

  * Cursor movement is sometimes slow because of the excessive redraw
    of overlapping/overlapped rows.
    http://lists.gnu.org/archive/html/emacs-devel/2005-09/msg00705.html

  * Tall characters get thicker because they are overdrawn when
    overlapping rows are redrawn.  This is the verical version of the
    following problem:
    http://lists.gnu.org/archive/html/emacs-devel/2005-01/msg00729.html

  * Sole diacritical marks and right-to-left texts are not displayed
    correctly.

  * A JISX0212 character in HELLO (C-h h) is not displayed by default.
    (I don't mean all of the remaining characters are displayed by
    default.)  A workaround is to evaluate
    (define-translation-hash-table 'ucs-mule-cjk-to-unicode
     ucs-mule-cjk-to-unicode).

                                     YAMAMOTO Mitsuharu
                                address@hidden