#3000 safe.test performance

[Don Porter]

I find that when running Tcl's
test suite, the safe.test file
always takes several minutes
to complete.

Looking into the details of this,
I find that the SafeBase [source]
alias is being force to deal with
hundreds of files, and this all derives
from an ::auto_path list with hundreds
of elements.

Basically every subdirectory of
/usr/local/lib ends up on the ::auto_path,
and on my system, that's a lot of files.

None of them appear to be important
to what's being tested in safe.test, so
the attached patch saves ::auto_path,
sets it to a bare minimum value, and
restores when safe.test tests are done.
Result is much faster.

[Don Porter]

[Don Porter]

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same technique also helps
Tk's safe.test

[Don Porter]

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committing for 8.5a2.