db, db.sqlite: If we are in a transaction, don't start another transaction. Add a unit test. Fixes #631. Fixes #623.

basis/db/db.factor

@@ -146,7 +146,11 @@ M: db-connection rollback-transaction ( -- ) "ROLLBACK" sql-command ;
 : in-transaction? ( -- ? ) in-transaction get ;
 
 : with-transaction ( quot -- )
-    t in-transaction [
-        begin-transaction
-        [ ] [ rollback-transaction ] cleanup commit-transaction
-    ] with-variable ; inline
+    in-transaction? [
+        call
+    ] [
+        t in-transaction [
+            begin-transaction
+            [ ] [ rollback-transaction ] cleanup commit-transaction
+        ] with-variable
+    ] if ; inline

basis/db/sqlite/sqlite-tests.factor

@@ -162,3 +162,13 @@ watch "WATCH" {
         user>> f user boa select-tuple
     ] with-db
 ] unit-test
+
+{ } [
+    test.db [ [
+            user ensure-table [
+                "mew" "foo" user boa insert-tuple
+                "denny" "kitty" user boa insert-tuple
+            ] with-transaction
+        ] with-transaction
+    ] with-db
+] unit-test