png_XYZ_from_xy_checked

by default.

(Clifford Yap)

to pngpriv.h (functions yet to be implemented).

The "_DLL" is removed from the test of whether a DLL is being built.

and fixed spelling (truely -> truly) in comments.

in libpng-1.5.4 and to mention recent CVE reports.

recognize the file extension, so it always compiles with C++ rules.  Made minor
changes to pngrutil.c to cast results where C++ expects it but C does not.

pnglibconf.h.prebuilt