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
diff --git a/configure.in b/configure.in
index e01408a..e3439f3 100644
--- a/configure.in
+++ b/configure.in
@@ -325,12 +325,14 @@
 
 dnl Checks for zlib library.
 
+WITH_ZLIB=0
 if test "$with_zlib" = "no"; then
     echo "Disabling compression support"
 else
     AC_CHECK_HEADERS(zlib.h,
 	AC_CHECK_LIB(z, gzread,[
-	    AC_DEFINE([HAVE_LIBZ], [], [Have compression library])
+	    AC_DEFINE([HAVE_LIBZ], [1], [Have compression library])
+	    WITH_ZLIB=1
 	    if test "x${Z_DIR}" != "x"; then
 		Z_CFLAGS="-I${Z_DIR}/include"
 		Z_LIBS="-L${Z_DIR}/lib -lz"
@@ -346,6 +348,7 @@
 
 AC_SUBST(Z_CFLAGS)
 AC_SUBST(Z_LIBS)
+AC_SUBST(WITH_ZLIB)
 
 CPPFLAGS=${_cppflags}
 LDFLAGS=${_ldflags}