save some space.

    contrib/pngminim project to pngerror.c, for use when warnings or
    errors are disabled via PNG_NO_WARN or PNG_NO_ERROR_TEXT, to avoid
    storing unneeded error/warning text.

not quite working yet (pow is undefined)

and fixed a small typo in a comment in pngconf.h

version that works with libpng-1.5.0 is received)

    In all prior versions of libpng most configuration options
    controlled by compiler #defines had to be repeated by the
    application code that used libpng.  This patch changes this
    so that compilation options that can only be changed at build
    time are frozen in the build.  Options that are compiler
    dependent (and those that are system dependent) are evaluated
    each time - pngconf.h holds these.  Options that can be changed
    per-file in the application are in png.h.  Frozen options are
    in the new installed header file pnglconf.h

to scripts/symbols.def, added scripts/checksym.*

against the new DEF file scripts/symbols.def.
Changed the default DEF file back to pngwin.def.
Removed makefile.mingw.