Enhanced xmlXPathRunStreamEval, fixed handling of depth/level for cases

* xpath.c, pattern.c: Enhanced xmlXPathRunStreamEval, fixed
  handling of depth/level for cases like union operator
  (bug #306348 reported by Bob Stayton).  Also enhanced
  several comments throughout pattern.c.
* doc/apibuild.py: fixed problem in handling of
  'signed' declaration.  Rebuilt the docs.
12 files changed