edited a couple of comments in accordance with posting on the mailing list

* xmlschemas.c: edited a couple of comments in accordance with
  posting on the mailing list (no logic change)
* xpointer.c: working on Bug 129967, added check for NULL
  nodeset to prevent crash.  Further work required.
* xpath.c: working on Bug 129967, added code to handle
  XPATH_LOCATIONSET in RANGETO code, also added code to
  handle it in xmlXPathEvaluatePredicateResult.  Further
  work required.
diff --git a/xmlschemas.c b/xmlschemas.c
index 60a5bce..e567337 100644
--- a/xmlschemas.c
+++ b/xmlschemas.c
@@ -356,7 +356,7 @@
 
 /**
  * xmlSchemaNewSchema:
- * @ctxt:  a schema validation context (optional)
+ * @ctxt:  a schema validation context
  *
  * Allocate a new Schema structure.
  *
@@ -402,7 +402,7 @@
 
 /**
  * xmlSchemaNewAnnot:
- * @ctxt:  a schema validation context (optional)
+ * @ctxt:  a schema validation context
  * @node:  a node
  *
  * Allocate a new annotation structure.