Spelling and grammar fixes

Fixes bug 743172, bug 743489, bug 769632, bug 782400 and a few other
misspellings.
diff --git a/debugXML.c b/debugXML.c
index a1b550a..a8ec8a4 100644
--- a/debugXML.c
+++ b/debugXML.c
@@ -2931,7 +2931,7 @@
 		  fprintf(ctxt->output, "\tvalidate     check the document for errors\n");
 #endif /* LIBXML_VALID_ENABLED */
 #ifdef LIBXML_SCHEMAS_ENABLED
-		  fprintf(ctxt->output, "\trelaxng rng  validate the document agaisnt the Relax-NG schemas\n");
+		  fprintf(ctxt->output, "\trelaxng rng  validate the document against the Relax-NG schemas\n");
 #endif
 		  fprintf(ctxt->output, "\tgrep string  search for a string in the subtree\n");
 #ifdef LIBXML_VALID_ENABLED