[libpng16] Imported from libpng-1.6.8rc01.tar
Bookkeeping: move functions around (no changes)
Move transform 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, the former MNG specific functions are
better placed in pngread/pngwrite.c

Signed-off-by: John Bowler <jbowler@acm.org>
Make transform implementation functions static
This makes the 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 easy changes to the
internal interfaces.

Signed-off-by: John Bowler <jbowler@acm.org>