Allow ClassAds to invoke python functions. #4773
Add protections to python_invoke. #4773

This introduces the CLASSAD_USER_PYTHON_MODULES configuration knob.
If set, the referenced python modules are loaded and made available
to the ClassAd library through the "python_invoke" function.  No
other modules are available; further, any functions starting with
"_" are disallowed.

With this, the sysadmin has fine-grained control over which
functions are available through ClassAds.
Documentation and version history for CLASSAD_USER_PYTHON_MODULES. #4773
Fix build issues from batlab. #4773
Make python exception / ClassAd error behavior consistent. #4773

python_invoke and registered functions previously had differing
behavior when a python exception is thrown.  Now, both functions
will *keep* the python exception set and return an error value.

This means the next time control returns to the python interpreter
(i.e., using python_invoke or register from a python script), an
exception is thrown.
Merge branch 'V8_3-gt4773'. #4773

Conflicts:
	doc/version-history/8-3.history.tex
fixing #4793 turn off copyright msg for mt.exe tool
(#4791)  Use the existin trim() function.
Merge remote-tracking branch 'origin/V8_2-branch'
(#4375)  *couhg*  Add the man page.  *cough*
Merge remote-tracking branch 'origin/V8_3_2-branch'
Merge branch 'master' into master-gt4613