removed some warnings by casting xmlChar to unsigned int and a couple of

* DOCBparser.c HTMLparser.c entities.c parser.c relaxng.c
  xmlschemas.c xpath.c: removed some warnings by casting xmlChar
  to unsigned int and a couple of others.
* xmlschemastypes.c: fixes a segfault on empty hexBinary strings
Daniel
diff --git a/entities.c b/entities.c
index 1886d53..67317f3 100644
--- a/entities.c
+++ b/entities.c
@@ -532,7 +532,7 @@
             ptr = buf;
 	    while (*ptr != 0) *out++ = *ptr++;
 #endif
-	} else if (IS_CHAR(*cur)) {
+	} else if (IS_CHAR((unsigned int) *cur)) {
 	    char buf[10], *ptr;
 
 	    snprintf(buf, sizeof(buf), "&#%d;", *cur);
@@ -731,7 +731,7 @@
 		cur += l;
 		continue;
 	    }
-	} else if (IS_CHAR(*cur)) {
+	} else if (IS_CHAR((unsigned int) *cur)) {
 	    char buf[10], *ptr;
 
 	    snprintf(buf, sizeof(buf), "&#%d;", *cur);