internal functions called by png_do_{read|write}_transformations static. On an
x86-64 DLL build (Gentoo Linux) this reduces the size of the text
segment of the DLL by 1208 bytes, about 0.6%. It also simplifies
maintenance by removing the declarations from pngpriv.h and allowing
easier changes to the internal interfaces.

function definitions before the place where they are called so that
they can be masde static. Move the intrapixel functions and the
grayscale palette builder out of the png?tran.c files. The latter
isn't a transform function and is no longer used internally, and the
former MNG specific functions are better placed in pngread/pngwrite.c

compiler issues slightly different warnings from those issued by the
current vesions of GCC. This eliminates those warnings by
adding/removing casts and small code rewrites.

Added new "png_structrp" typedef. Because of the
way libpng works both png_info and png_struct are always accessed via a
single pointer.  This means adding C99 'restrict' to the pointer gives
the compiler some opportunity to optimize the code.  This change allows that.

Fixed some compiliation problems with scaling options.

handling. Internal changes only except for a new option to avoid compiling
in the png_build_grayscale_palette API (which is not used at all internally.)
The main change is to move the transform tests (READ_TRANSFORMS,
WRITE_TRANSFORMS) up one level to the caller of the APIs.

that was introduced in libpng-1.5.2beta01.

Certain optional gcc warning flags resulted in warnings in libpng code.
With these changes only -Wconversion and -Wcast-qual cannot be turned on.
Changes are trivial rearrangements of code.  -Wconversion is not possible
for pngrutil.c (because of the widespread use of += et al on variables
smaller than (int) or (unsigned int)) and -Wcast-qual is not possible
with pngwio.c and pngwutil.c because the 'write' callback and zlib
compression both fail to declare their input buffers with 'const'.

that CCP writes to standard output by default (Martin Banky).

Studio 2010 (John Bowler).

literal pointers declare them (John Bowler).
Many APIs did not change their arguments but were not declared using
PNG_CONST.  This change corrects this.  In a few cases APIs that return
constant string literal pointers have also been changed to declare this.
Unlike the argument change this may require app changes; however the
results could never be written to (the app would crash on some platforms
where strings are not writable), so this seems advisable.