small changes to some error messages; greatly expanded builtins tests

tests/comsub.tests

@@ -91,6 +91,15 @@ read << EOC
 Dir: ${BUILDDIR#<(echo a)/}
 EOC
 
+# return in a comsub inside a shell function should abort the comsub
+func()
+{
+	local v
+	v=$( echo comsub ; return ; echo after)
+	echo $FUNCNAME: v = $v
+}
+func
+
 ${THIS_SH} ./comsub1.sub
 ${THIS_SH} ./comsub2.sub
 ${THIS_SH} ./comsub3.sub