(activate-mark): Set transient-mark-mode buffer-locally.
(transient-mark-mode): Use&set the global value.
* lisp/mouse.el (mouse-set-region-1, mouse-drag-track): Idem.
* lisp/org/org-compat.el (activate-mark): Idem.
* lisp/emulation/edt.el (edt-emulation-off): Save&restore the global
transient-mark-mode setting.
* lisp/obsolete/pc-select.el (pc-selection-mode): Use the
transient-mark-mode function.
Fixes: debbugs:6316
Remove the mark/nomark handling, and activate shift-select-mode instead.
* lisp/obsolete/pc-mode.el: Rename from emulation/pc-mode.el.
Fixes: debbugs:7940