[libpng17] Updated CHANGES and ANNOUNCE, fixed typo in pngunknown.c comment.

CHANGES

@@ -5511,11 +5511,31 @@ Version 1.7.0beta77 [January 16, 2016]
     there is an unrelated bug which means that lower zlib memLevels result
     in memory corruption under some circumstances, probably less often
     than 1:1000.
-  Worked around a false-positive Coverity issue in pngvalid.c.
+  Attempted to work around a false-positive Coverity issue in pngvalid.c.
 
-Version 1.7.0beta78 [January 17, 2016]
+Version 1.7.0beta78 [January 19, 2016]
   Changed PNG_USE_MKSTEMP to __COVERITY__ to select alternate
     "tmpfile()" implementation in contrib/libtests/pngstest.c
+  Fixed NO_STDIO build of pngunknown.c to skip calling png_init_io()
+    if there is no stdio.h support.
+  Added an API and a number of assist macros to allow an application
+    that uses the simplified API write to bypass stdio and write
+    directly to memory.
+  Added some warnings (png.h) and some check code to detect *possible*
+    overflow in the ROW_STRIDE and simplified image SIZE macros.  This
+    disallows image width/height/format that *might* overflow.  This is
+    a quiet API change that limits in-memory image size (uncompressed) to
+    less than 4GByte and image row size (stride) to less than 2GByte.
+  Revised  Simplified API to use system appropriate types.  This is
+    an API change for 1.7, albeit a quiet one; it may produce compiler
+    warnings but should not result in errors, unless warnings are treated
+    as errors. On 64-bit systems it widens the results of the various
+    PNG_IMAGE_ macros that return size values (component counts, byte sizes)
+    to 64 bits.  It also changes the row_stride parameter, which is the
+    pointer difference between adjacent rows of the image buffer, to
+    the ANSI-C90 defined type ptrdiff_t. The existing (1.6.22) checks for
+    overflow are preserved but now accomodate images that require more than
+    32 bits of address space when size_t/ptrdiff_t are 64 bit types.
 
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