Merged libpng-1.2.41.txt with libpng-1.4.0.txt where appropriate.

into the main libpng directory.  More bugfixes and improvements to
CMakeLists.txt (Philip Lowman)

from pngwrite.c

and png_set_user_cache_max() from libpng-1.4.0rc01.

    png_calloc(), png_get_io_state(),
    png_get_io_chunk_name(), png_set_premultiply_alpha, and
    png_do_read_premultiply_alpha().

changing "#if defined(x)" to "#ifdef x" in png.h and pngconf.h.

everywhere except pngconf.h as in libpng-1.4.0beta78 and later.

that was inadvertently deleted by the previous checkin.

from libpng-1.4.0beta87.

from libpng-1.4.0beta87.

from libpng-1.4.0beta87

from libpng-1.4.0beta87

from libpng-1.4.0beta87

from libpng-1.4.0beta87.

changing many "#if defined(x)" to "#ifdef x".

changing many "#if defined(x)" to "#ifdef x" in pngtest.c and pngwutil.c.

by defining PNG_iTXT_SUPPORTED

of "pp" in png_handle_sPLT().

from libpng.0.dylib to libpng.3.dylib to be consistent with makefile.darwin.

similar one already in libpng-1.4.0beta (Alam Arias).