Change default exit status of usage_is to 2

Similar to grep or test, 1 is reserved for "no", 2 is used for
"incorrect use/syntax"

include/core.sh

 
 usage_is() {
     #
-    # Echo out usage patterns and (by default) exit 1
+    # Echo out usage patterns and (by default) exit 2
     #
     # Specify -e STATUS for exit status, or "-E" to prevent
     # exiting.  Use "--" to delimit end of arguments processed
     # Recommended usage is to define usage() in your script and
     # use this in body.
     #
-    local es=1
+    local es=2
     while true; do case "$1" in
         -e) es="$2"; shift 2 ;;
         -E) es="";   shift   ;;