Throughout, change fhandler_*::read and fhandler_*::raw_read to void functions

whose second arguments are both the lenght and the return value.
* fhandler.cc (fhandler_base::read): Rework slightly to use second argument as
input/output.  Tweak CRLF stuff.
(fhandler_base::readv): Accommodate fhandler_*::read changes.
* cygthread.h (cygthread::detach): Declare as taking optional handle argument.
(cygthread::detach): When given a handle argument, wait for the handle to be
signalled before waiting for thread to detach.  Return true when signal
detected.

winsup/cygwin/fhandler_zero.cc

@@ -35,11 +35,11 @@ fhandler_dev_zero::write (const void *, size_t len)
   return len;
 }
 
-int __stdcall
-fhandler_dev_zero::read (void *ptr, size_t len)
+void __stdcall
+fhandler_dev_zero::read (void *ptr, size_t& len)
 {
   memset (ptr, 0, len);
-  return len;
+  return;
 }
 
 __off64_t