Make use of usage errors from newer pretty.sh

src/libexec/dottum-install

@@ -8,7 +8,7 @@ shellfu import dottum
 shellfu import saturnin
 
 usage() {
-    mkusage "[options] VAULT [SUBVAULT]" \
+    mkusage "$@" "[options] VAULT [SUBVAULT]" \
         -o \
         "-n     Do not do anything, just show what would be done" \
         "-B     Do not replace broken link"                       \
@@ -18,7 +18,7 @@ usage() {
 dottum__route() {
     local Vault=$1; shift
     local SubVaults=()
-    test -n "$Vault" || usage
+    test -n "$Vault" || usage -w "no VAULT?"
     test -e "$Vault" || die "vault does not exist: $Vault"
     test -d "$Vault" || die "vault is not a directory: $Vault"
     SubVaults=("$@")