patched to redirrect all "out of context" error messages to

a reconfigurable routine. The changes are:
* xmlerror.h : added the export of an error context type (void *)
  an error handler type xmlGenericErrorFunc there is an interface
  xmlSetGenericErrorFunc(void *ctx, xmlGenericErrorFunc handler);
  to reset the error handling routine and its argument
  (by default it's equivalent to respectively fprintf and stderr.
* all the c files: all wild accesses to stderr or stdout within
  the library have been replaced to calls to the handler.
Daniel

testHTML.c

@@ -40,6 +40,7 @@
 #include <libxml/HTMLparser.h>
 #include <libxml/HTMLtree.h>
 #include <libxml/debugXML.h>
+#include <libxml/xmlerror.h>
 
 #ifdef LIBXML_DEBUG_ENABLED
 static int debug = 0;
@@ -719,7 +720,8 @@ void parseAndPrintFile(char *filename) {
 	doc = htmlParseFile(filename, NULL);
     }
     if (doc == NULL) {
-        fprintf(stderr, "Could not parse %s\n", filename);
+        xmlGenericError(xmlGenericErrorContext,
+		"Could not parse %s\n", filename);
     }
 
     /*