added the routine xmlNanoHTTPContentLength to the external API

* nanohttp.c, include/libxml/nanohttp.h: added the routine
  xmlNanoHTTPContentLength to the external API (bug151968).
* parser.c: fixed unnecessary internal error message (bug152060);
  also changed call to strncmp over to xmlStrncmp.
* encoding.c: fixed compilation warning (bug152307).
* tree.c: fixed segfault in xmlCopyPropList (bug152368); fixed
  a couple of compilation warnings.
* HTMLtree.c, debugXML.c, xmlmemory.c: fixed a few compilation
  warnings; no change to logic.
diff --git a/encoding.c b/encoding.c
index e3ca7d8..e05c375 100644
--- a/encoding.c
+++ b/encoding.c
@@ -2132,7 +2132,7 @@
 	 */
         if (in->end - in->cur > 0) {
 	    static unsigned char convbuf[32000];
-	    unsigned const char *cur = (unsigned const char *)in->cur;
+	    const unsigned char *cur = (const unsigned char *)in->cur;
 	    int toconv = in->end - in->cur, written = 32000;
 
 	    int ret;