Merged revision(s) 1569991, 1615720, 1615731, 1615780-1615781, 1615893, 1589759 from poi/trunk:
Apply suggestions from Uwe Schindler for more secure xml defaults for #54764 and #56164, for xml parsers which support them
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Add another test file for #54764, and a test that uses it
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Change the default XMLBeans version used for running to be 2.6, leave 2.3 for compiling the schemas (for maximum compatibility)
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Before parsing an OOXML document, reset the xmlbeans sax parser to avoid the risk of getting one in an error state (due to XMLBEANS-512). Should be a minimal extra overhead pending a proper fix. Allows us to finish enabling the unit tests for #54764
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Correct xmlbeans 2.6 url

git-svn-id: https://svn.apache.org/repos/asf/poi/branches/REL_3_10_BRANCH@1616509 13f79535-47bb-0310-9956-ffa450edef68