This version of autogen.sh attempts to dissuade people from running it when
it is not, or should not, be necessary.

(C. Yapp).

in CMakeLists.txt

instead of running tools one-by-one.

Also some layout regularization and removal of introduced tab characters
(replaced with 3-character indentation).  Obsolete macros identified by
autoupdate have been removed; the replacements are all in 2.59 so
the pre-req hasn't been changed.  --enable-werror checks for support
for -Werror (or the given argument) in the compiler.  This mimics the
gcc configure option by allowing -Werror to be turned on safely; without
the option the tests written in configure itself fail compilation because
they cause compiler warnings.

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.

This is an initial version for review; the documentation has not yet been
updated.

changes some of the macro definitions in png.h, app code may need
corresponding changes.

truncated (bug introduced in libpng-1.5.3beta05).

and cleaned up some indentation problems.

when png_uint_32 and unsigned long are of different sizes.

those uses of png_memcpy that were doing a simple assignment to assignments
(all those cases where the thing being copied is a non-array C L-value.)
Added some error checking to png_set_*() routines and removed the
reference to the non-exported function png_memcpy() from example.c. Fixed
the Visual C 64-bit build - it requires jmp_buf to be aligned, but it had
become misaligned.

 Because these APIs store to the png_info they can take a
 png_const_structrp now that the error routines also accept
 one of these.

to the proper location in configure.ac (Gilles Espinasse).

It was not actually possible to use it uninitialized but gcc doesn't know that.

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.

Previously it was disabled whenever internal fixed point arithmetic was
selected, which meant it didn't exist even on systems where FP was available
but not preferred.

and only calls one other internal function and memset.

changes alter how the tricky allocation of the initial png_struct and png_info
structures are handled. png_info is now handled in pretty much the same
way as everything else, except that the allocations handle NULL return
silently.  png_struct is changed in a similar way on allocation and on
deallocation a 'safety' error handler is put in place (which should never
be required).  The error handler itself is changed to permit mismatches
in the application and libpng error buffer size; however, this means a
silent change to the API to return the jmp_buf if the size doesn't match
the size from the libpng compilation; libpng now allocates the memory and
this may fail.  Overall these changes result in slight code size
reductions; however, this is a reduction in code that is always executed
so is particularly valuable.  Overall on a 64-bit system the libpng DLL
decreases in code size by 1733 bytes.  pngerror.o increases in size by
about 465 bytes because of the new functionality.