merge trunk
merge trunk: INST_TAILCALL has bug
Create Tcl 8.6.0 release branch
Declare TclOO portion of the Tcl API to be stable -> TclOO 1.0
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Allow http, msgcat and tcltest to be loaded by Tcl 9 as well. I think
that this should be included in tcl8.6.0: Those 3 packages are so
widely used, we don't want to introduce Tcl-level incompatibilities
in Tcl9 such that those packages wouldn't work any more.
merge trunk
Fix gcc warning in cygwin build: implicitely declared function TclUnixOpenTemporaryFile. 
Move the function to slot 30, and define it (as 0) for win32 as well.
merge trunk
Change TCL_VERSION to "8.6-" everywhere in Tcl_InitStubs. This is not the way how to do it! Just for testing purposes.
use Tcl_PkgProvideEx everywhere (again, for testing purposes)
do some Tcl_EvalEx, for test-purposes, demonstrating a crash
Tcl_InitStubs("8.5",1) would succeed in an "8.50" interp.  Fixed.