[libpng15] Fixed typos in the manual and in scripts/pnglibconf.dfa

(CFLAGS -> CPPFLAGS and PNG_USR_CONFIG -> PNG_USER_CONFIG).
[libpng15] Imported from libpng-1.5.19beta01.tar
[libpng15] Bump version to 1.5.19beta02
[libpng15] Update "last changed date" in pngrtran.c
[libpng15] Removed unused PNG_CALLOC_SUPPORTED from scripts/pnglibconf.dfa

and script/pnglibconf.h.prebuilt
[libpng15] Use "if (value != 0)" instead of "if (value)" consistently.
[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
[libpng15] Fixed a typo in pngrutil.c, introduced in libpng-1.5.6, that

interferes with "blocky" expansion of sub-8-bit interlaced PNG files.
[libpng15] Imported from libpng-1.5.19beta03.tar
[libpng15] Bump version to 1.5.19beta04
[libpng15] Updated CHANGES file with some January 2013 CVE numbers.
[libpng15] Removed scripts/makefile.elf which has not worked since libpng-1.4.x
[libpng15] Imported from libpng-1.5.19beta04.tar