[libxml2] Fix compilation with minimum and schematron.

[Daniel Veillard <veillard src gnome org>]

commit 1af8b7b22e3bb569b2c27642064224bc14a1924a
Author: Nicolas Le Cam <niko lecam gmail com>
Date:   Fri Jun 14 22:20:37 2013 +0200

    Fix compilation with minimum and schematron.
    
    Add a hard dependancy on tree.
    Disable write and close callbacks when output is disabled.

 configure.in |    1 +
 schematron.c |    2 ++
 2 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/configure.in b/configure.in
index 7374564..ecaa403 100644
--- a/configure.in
+++ b/configure.in
@@ -223,6 +223,7 @@ fi
 if test "$with_schematron" = "yes"
 then
     with_pattern=yes
+    with_tree=yes
     with_xpath=yes
 fi
 if test "$with_reader" = "yes"
diff --git a/schematron.c b/schematron.c
index 537b868..eb4befe 100644
--- a/schematron.c
+++ b/schematron.c
@@ -165,8 +165,10 @@ struct _xmlSchematronValidCtxt {
 
     FILE *outputFile;          /* if using XML_SCHEMATRON_OUT_FILE */
     xmlBufferPtr outputBuffer; /* if using XML_SCHEMATRON_OUT_BUFFER */
+#ifdef LIBXML_OUTPUT_ENABLED
     xmlOutputWriteCallback iowrite; /* if using XML_SCHEMATRON_OUT_IO */
     xmlOutputCloseCallback  ioclose;
+#endif
     void *ioctx;
 
     /* error reporting data */