Revert much of previous erroneous checkin. Add ChangeLog entry.

* pinfo.h: Correctly set __SIGOFFSET.
* path.cc (hash_path_name): Avoid calling library functions for simple copying
of characters.
* shortcut.c: Use WIN32_LEAN_AND_MEAN.
* smallprint.c: Ditto.
* environ.cc (getwinenv): Minor clarity fix.
* localtime.c: No need to include windows.h
* string.h: New file.

winsup/cygwin/pinfo.h

@@ -15,7 +15,7 @@ enum
   __SIGFLUSH	    = -2,
   __SIGSTRACE	    = -1,
   __SIGUNUSED	    =  0,
-  __SIGOFFSET	    =  2
+  __SIGOFFSET	    =  3
 };
 
 #define PSIZE 63