Fix typos on CHANGES

CHANGES

@@ -4,7 +4,7 @@ The following are the changes from calc version 2.13.0.1 to date:
 
     The ${PREFIX} is not the same as ${T}.  The ${T} specifies
     a top level directory under which calc installs things.
-    While usally ${T} is empty, it can be specific path
+    While usually ${T} is empty, it can be specific path
     as if calc where "chrooted" during an install.
     The ${PREFIX} value, during install, is a path between
     the top level ${T} install directory and the object
@@ -14,7 +14,7 @@ The following are the changes from calc version 2.13.0.1 to date:
 
     Added Makefile.local, a file with a single comment.  The main
     Makefile includes Makefile.local just before the first all rule.
-    One may overtide any Makefile setting by modifying Makefile.local.
+    One may override any Makefile setting by modifying Makefile.local.
     For example, Makefile.local could force BLD_TYPE:
 
 	HAVE_STRING_H:= YES