memcpy() with a null source, even if count is zero (Leon Scroggins III).

positions.  Fixed the sequential reader to handle these more robustly
(John Bowler).

properly (patch by Timothy Nikkel).

presence of clock_gettime() in configure.ac and Makefile.am.

on platforms that don't supply clock_gettime().

    Added support to use multiple directories in ZLIBINCDIR variable,
    Fixed CMAKE_C_FLAGS with multiple values when genout is compiled on MSVC,
    Fixed pnglibconf.c compilation on OS X including the sysroot path.

(Bug report by Y.Ohashik).

PNG_FILTER_NONE|PNG_FILTER_SUB|PNG_FILTER_UP).