Fixed type conversion warnings which break a Win32 debug build (MSVC).
Accommodate the "udp" package, and any other Tcl package that expects a
[read] on a channel @ EOF to attempt another pass through the channel drivers
instead of immediately returning an empty string.  Correcting this misbehavior
appears too disruptive in a patch release to a long stable branch.
merge-mark.  Do not accommodate udp bugs in Tcl 8.6.2.
merge trunk