Ensure all open dbs are closed when exiting the test server

Prevents file in use errors when running the test-suite on windows

src/calibre/srv/handler.py

@@ -60,6 +60,10 @@ class LibraryBroker(object):
                     raise
             return ans
 
+    def close(self):
+        for db in self.lmap.itervalues():
+            db.close()
+        self.lmap = {}
 
 class Context(object):
 
@@ -137,3 +141,6 @@ class Handler(object):
     def set_log(self, log):
         self.router.ctx.log = log
 
+    def close(self):
+        self.router.ctx.library_broker.close()
+

src/calibre/srv/tests/base.py

@@ -137,3 +137,7 @@ class LibraryServer(TestServer):
         )
         self.handler.set_log(self.loop.log)
         specialize(self)
+
+    def __exit__(self, *args):
+        self.loop.stop()
+        self.handler.close()