* xpath.c: Applied patch from Rob Richards, fixing a potential
  memory leak in xmlXPathTryStreamCompile(), when a list of
  namespaces was assigned to the XPath compilation context;
  here a new namespace list was created and passed to
  xmlPatterncompile(); but this list was not freed afterwards.
  Additionally we avoid now in xmlXPathTryStreamCompile() to
  compile the expression, if it has a colon - indicating
  prefixed name tests - and no namespace list was given. The
  streaming XPath mechanism needs a namespace list at
  compilation time (unlike normal XPath, where we can bind
  namespace names to prefixes at execution time).
* pattern.c: Enhanced to use a string dict for local-names,
  ns-prefixes and and namespace-names.
  Fixed xmlStreamPushInternal() not to use string-pointer
  comparison if a dict is available; this won't work, since
  one does not know it the given strings originate from the
  same dict - and they normally don't do, since e.g.
  namespaces are hold on xmlNs->href. I think this would be
  worth an investigation: if we can add a @doc field to xmlNs
  and put the @href in to a additionan namespace dict hold
  in xmlDoc. Daniel will surely not like this idea :-) But
  evaluation of tons of elements/attributes in namespaces
  with xmlStrEqual() isn't the way we should go forever.