[XML-SIG] character enitity references in ESIS DOM builder

[Pieter Nagel]

Currently, xml/dom/esis_builder.py has only a small hardcoded map to
transform only 11 of the ISOlat1 entity references to their ISO8859-1
representation.

I have a patch to do the following:

1) make the SDATA map user extensible
2) make unknown entity references an error, instead of silently
injecting "unknown" into the line *
3) move the global methods in the file into the class (needed for 1)
4) Very minor speedup (currently a regular expression is being
recompiled twice for each line of ESIS data, instead of once per
builder instantiation).
5) Code cleanup (meaningfull identifiers, remove commented dead code)

Who should I send this to?

* This has nasty effects on foreign text. As the sage said: "My
ounknown wil dit nie hunkown en ek sunkown ook nunkownnunknown vir
julle stop dit!"
--

  Pieter Nagel