Add <<Invoke>> bindings to button, listbox and menu, for consistancy with ttk.
Add documentation for <<EnteredChild>>, <<Invoke>>, <<Increment>> and <<Decrement>>
[Bug 3608074]: Add <<Invoke>> bindings to Button's, Listbox and Menu.
Document <<Invoke>>, <<ThemeChanged>>, <<EnteredChild>> (ttk_pandedwindow only) and <<Increment/Decrement>> (ttk_spinbox only)
Same change as [9bc120ced2] for UNIX, but for Windows as well.
Make compiling/running Tk8.5 against 8.6 headers work on Windows as well.
In dynamic builds, Tcl_FindExecutable should always be taken from the stub table, even though the 8.6 headers tell otherwise. That's why in Tcl 8.6, the Tcl_FindExecutable() call moved from Tk_MainEx to the Tk_Main() macro.
Properly clean up, when a (Tcl 8.6) thread is canceled.
Easier solution, with proper protection and configure warnings.
One last review of tkCmds.c, making sure that there is no single mistake in it. 
Found one unnecessary IncrRefCount/DecrRefcount, some unneeded type cast and a few more cleanups, all already fixed in Tk 8.6. So better backport that too.
Backout [ea8d772054] and [9bc120ced2]
Cherry-pick [14a41a1d96]
merge-mark