Change one '#ifdef' to '#if defined()' for improved consistency within the file,
as in checkin [211aa43013].
Exceptional handling of oo::class has to be consistent throughout.
Refine TclFinalizeThreadData so that the quick-exit optimization really only affects exit.
[84af1192f5]: [regsub] compiler no longer confused by quantification handling.
[2486824] Improve error message; not all that upvars is an upvar.
[2486824] Improve error message; not all that upvars is an upvar.
[cee90e4e88] Correct error in stack depth checking.
Developed an improved bootloader built around TclSetPreInitScript. The new bootloader
now mounts the VFS before the interpreter is initialized, and gives it enough
hints to point to the VFS for init.tcl and main.tcl (If present)

Also, Tcl_ZVfs_Boot now takes and additional argument: the name of the file to mount.

As the difference between a normal shell and a zvfs enabled shell is one again, several
lines of code, the example shells is folded back into tclAppInit.c and controlled with
macros.

The ZVFS commands are now loaded in as a static package.

Removed the Stubs emtry for Tcl_Boot_ZVFS, it's now intended that shells build
their own copy of tclZipVfs.o
Merging in changes from trunk