'with-store' and 'with-database' and written in terms of 'unwind-protect'.

* src/cuirass/base.scm (with-store): Rewrite using 'unwind-protect'.
* src/cuirass/database.scm (with-database): Likewise.

src/cuirass/base.scm

@@ -67,19 +67,18 @@
   ;; currently closes in a 'dynamic-wind' handler, which means it would close
   ;; the store at each context switch.  Remove this when the real 'with-store'
   ;; has been fixed.
-  (let* ((store (open-connection))
-         (result (begin
-                   ;; Always set #:keep-going? so we don't stop on the first
-                   ;; build failure.  Set #:print-build-trace explicitly to
-                   ;; make sure 'process-build-log' sees build events.
-                   (set-build-options store
-                                      #:use-substitutes? (%use-substitutes?)
-                                      #:fallback? (%fallback?)
-                                      #:keep-going? #t
-                                      #:print-build-trace #t)
-                   exp ...)))
-    (close-connection store)
-    result))
+  (let ((store (open-connection)))
+    (unwind-protect
+     ;; Always set #:keep-going? so we don't stop on the first build failure.
+     ;; Set #:print-build-trace explicitly to make sure 'process-build-log'
+     ;; sees build events.
+     (set-build-options store
+                        #:use-substitutes? (%use-substitutes?)
+                        #:fallback? (%fallback?)
+                        #:keep-going? #t
+                        #:print-build-trace #t)
+     exp ...
+     (close-connection store))))
 
 (cond-expand
   (guile-2.2

src/cuirass/database.scm

@@ -253,10 +253,8 @@ INSERT INTO Evaluations (specification, revision) VALUES ("
   ;; XXX: We don't install an unwind handler to play well with delimited
   ;; continuations and fibers.  But as a consequence, we leak DB when BODY
   ;; raises an exception.
-  (let* ((db (db-open))
-         (result (begin body ...)))
-    (db-close db)
-    result))
+  (let ((db (db-open)))
+    (unwind-protect body ... (db-close db))))
 
 (define* (read-quoted-string #:optional (port (current-input-port)))
   "Read all of the characters out of PORT and return them as a SQL quoted