applied patch from Andrew W. Nosenko to expose if zlib support was

* configure.in parser.c xmllint.c include/libxml/parser.h
  include/libxml/xmlversion.h.in: applied patch from Andrew W. Nosenko
  to expose if zlib support was compiled in, in the header, in the
  feature API and in the xmllint --version output.
Daniel

include/libxml/parser.h

@@ -1206,6 +1206,7 @@ typedef enum {
     XML_WITH_DEBUG = 28,
     XML_WITH_DEBUG_MEM = 29,
     XML_WITH_DEBUG_RUN = 30,
+    XML_WITH_ZLIB = 31,
     XML_WITH_NONE = 99999 /* just to be sure of allocation size */
 } xmlFeature;