XMLSchema.py

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   fixed an obvious bug, added a SchemaError class so it can actually
be thrown.


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commit a little while ago. :)  That is, wstools is now independant
of SOAPpy and ZSI.  This commit does the following:
    wstools/ServiceProxy.py is now ZSI/ServiceProxy.py, so some
    imports and ZSI docs had to change.
ZSI needs some changing, in case I didn't patch up all the imports
right.

(which doesn't), so that SOAPpy can use wstools without needing ZSI
around...  which is kinda the point of generic common-code. :)

    class SOAPCallInfo:
    class ParameterInfo:
    class HeaderInfo(ParameterInfo):
    def callInfoFromWSDL(port, name):
Next step is to move what's left of wstools/ServiceProxy.py into the ZSI
module (and fix up the imports), so that wstools has *no* soap-stack-specific
code in it.