librpc/spoolss: Fix undefined security_descriptor

spoolss.idl: cpp_quote("#define spoolss_security_descriptor security_descriptor")

The C Preprocessor understand that block, but PIDL Compiler don't, generating
incorrect code. All occurrences was renamed to security_descriptor.

Fábio Ramon
pidl: Supports converting string_array type

Added helper functions PyList_FromStringArray and PyList_AsStringArray to
convert IDL string_array type

Fábio Ramon
pidl: Add error information on Python Exception

Error handling in python was improved by passing the object returned on rpc call
inside the exception.

That feature allows, by example, verifying the buffer size needed by that call.

Fábio Ramon