The APNG patch for v1.6.47 isn't out yet, so I hacked in some changes
to get the APNG code to build in pngrutil.c. In particular, the PNGv3
chromacity changes also modified pngrutil.c to use table-based dispatch
instead of an if/else. png_read_frame_head() doesn't use this yet, so
the APNG functions in pngrutil.c haven't been marked static yet, but
they do now return png_handle_result_code.
TODO: Rebase using the APNG patch once it's rebased for v1.6.47.
NOTE: PNGv3 apparently makes APNG part of the specification, so
libpng "should" gain built-in support for APNG without a patch at
some point.
Note that two new functions were added to the original libpng, so the
ordinals for APNG were shifted over by two. This shouldn't be a problem,
since programs should be accessing functions by name instead of by
ordinal in 2017.
I've decided to get rid of the GDI+ PNG handling. It doesn't improve
anything performance-wise, adds coding overhead, and probably isn't
any faster than libpng.
GDI+ also doesn't support APNG. This version does.
NOTE: If I add APNG export, I'll need to use the included libpng
in Ubuntu builds, since Ubuntu still has libpng-1.2, and it's a
version that doesn't support APNG.
Reworked the bundled library system to be similar to the one in
mcrecover, but improved.
Added "-fpic -fPIC" to all extlib static libraries when building
for Linux systems. This is needed for libpng, but might not be
needed for other libraries; nevertheless, it should be set.
TODO: Use libpng in the Windows build. It's being linked in,
but it isn't actually being used for anything yet.
