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/cygthread.h

@@ -27,7 +27,7 @@ class cygthread
   cygthread (LPTHREAD_START_ROUTINE, LPVOID, const char *);
   cygthread () {};
   static void init ();
-  void detach (bool = false);
+  bool detach (HANDLE = NULL);
   operator HANDLE ();
   static bool is ();
   void * operator new (size_t);