Release note update

RELEASES.txt

@@ -394,6 +394,10 @@ Planned
 * Portability fixes for MSVC, avoid secure CRT warnings to work better with
   Windows Store apps
 
+* Portability fix for avoiding potentially non-portable signed integer
+  constants internally (e.g. use 0x7fffffffL - 1L instead of -0x80000000L);
+  this fixed a concrete problem with at least VS2010 + x64
+
 * Portability fixes for uclibc, use a replacement for e.g. fpclassify()
   because it is broken in some uclibc versions still in use (affected at
   least some mixed endian ARM environments)