Throughout, change check for running under Windows NT to 'iswinnt'.

* dcrt0.cc (set_os_type): Set 'iswinnt' appropriately.
* cygheap.cc (init_cheap): Revert to using VirtualAlloc for allocating cygheap.
(cygheap_setup_for_child_cleanup): New function.  Standard function to call
after calling CreateProcess to cleanup cygheap info passed to child.
(cygheap_fixup_in_child): Copy cygheap from shared memory into allocated space
under Windows 9x or if can't relocate shared space under NT.
* cygheap.h: Declare new function.
* spawn.cc (spawn_guts): Use cygheap_fixup_in_child.
* fork.cc (fork_parent): Ditto.
* winsup.h: Declare iswinnt.

winsup/cygwin/fhandler.h

@@ -418,7 +418,7 @@ public:
   /* This strange test is due to the fact that we can't rely on
      Windows shells to "do the right thing" with pipes.  Apparently
      the can keep one end of the pipe open when it shouldn't be. */
-  BOOL is_slow () {return os_being_run == winNT;}
+  BOOL is_slow () {return iswinnt;}
   select_record *select_read (select_record *s);
   select_record *select_write (select_record *s);
   select_record *select_except (select_record *s);