[libxml2] Fix a portability issue on Windows

[Daniel Veillard <veillard src gnome org>]

commit 190a0b89395f397b40aea02de6f362290ad6cc3d
Author: Longstreth Jon <Jon Longstreth mts com>
Date:   Thu Feb 6 10:58:17 2014 +0100

    Fix a portability issue on Windows
    
    Apparently an verflow when comparing macro and unsigned long

 parser.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/parser.c b/parser.c
index d61c216..0bf1aa2 100644
--- a/parser.c
+++ b/parser.c
@@ -2039,8 +2039,11 @@ static void xmlSHRINK (xmlParserCtxtPtr ctxt) {
        xmlGROW (ctxt);
 
 static void xmlGROW (xmlParserCtxtPtr ctxt) {
-    if ((((ctxt->input->end - ctxt->input->cur) > XML_MAX_LOOKUP_LIMIT) ||
-         ((ctxt->input->cur - ctxt->input->base) > XML_MAX_LOOKUP_LIMIT)) &&
+    unsigned long curEnd = ctxt->input->end - ctxt->input->cur;
+    unsigned long curBase = ctxt->input->cur - ctxt->input->base;
+
+    if (((curEnd > (unsigned long) XML_MAX_LOOKUP_LIMIT) ||
+         (curBase > (unsigned long) XML_MAX_LOOKUP_LIMIT)) &&
          ((ctxt->input->buf) && (ctxt->input->buf->readcallback != (xmlInputReadCallback) xmlNop)) &&
         ((ctxt->options & XML_PARSE_HUGE) == 0)) {
         xmlFatalErr(ctxt, XML_ERR_INTERNAL_ERROR, "Huge input lookup");