#496 struct::stack name collisions

[Will Duquette]

The command ::struct::stack generates a new stack object with an
automatically generated name. If the automatically generated
name is the name of an existing command, ::struct::stack throws
an error instead of automatically generating a unique name.

The only way to protect against this is to specify the name
explicitly, which works; however, it's an undocumented feature.

[Andreas Kupries]

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Right. Worse, the stack object command is always in the
global namespace. Graph for example on the other hand
generates in the callers namespace first. Definitely in need
of an update. Still the first/old style of command
generation. I believe I will add serialization as well
(trivial for stack). Maybe enough to go v2 for that package.