[Tcl] Made constant PMCs copy any strings they contain to constant strings, to work around the marking problem with constant PObjs that contain non-constant PObjs.
[Tcl] Made constant PMCs copy any strings they contain to constant strings, to
work around the marking problem with constant PObjs that contain non-constant
PObjs.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@26168 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot