* pattern.c, xpath.c, include/libxml/pattern.h: Further
  enhancement for XPath streaming, consolidated with
  schemas usage of pattern.c.  Added a new enum
  xmlPatternFlags.
* doc/*, testapi.c, elfgcchack.h: updated to reflect new
  enum.
* test/XPath/tests/mixedpat, test/XPath/docs/mixed,
  result/XPath/mixedpat: added regression test for problems
  reported in bug306348