[libpng15] Moved configuration information from the manual to the INSTALL file.
[libpng15] Imported from libpng-1.5.19beta02.tar
[libpng15] Bump version to 1.5.19beta03
[libpng15] Removed #if/#else/#endif from inside two pow() calls in pngvalid.c

because they were handled improperly by Portland Group's PGI-14.1 - PGI-14.3
when using its "__builtin_pow()" function.
[libpng15] Mention scripts/pnglibconf.h.prebuilt in INSTALL.
[libpng15] Port recent changes from libpng-1.6.11beta

  Silence 'unused parameter' build warnings (Cosmin).
  $(CP) is now used alongside $(RM_F).  Also, use 'copy' instead
    of 'cp' where applicable, and applied other minor makefile changes.
  Don't warn about invalid dimensions exceeding user limits.
[libpng15] Allow an easy replacement of the default pre-built configuration

header with a custom header, via the make PNGLIBCONF_H_PREBUILT macro.
[libpng15] Fix syntax of Copy command in makefile.amiga