Report the identity of the connection we're trying to establish.

This is more useful than parroting the lower level exception message, which
will already be shown in the full stack dump anyway.

src/main/java/com/samskivert/depot/PersistenceContext.java

@@ -555,7 +555,8 @@ public class PersistenceContext
         try {
             conn = _conprov.getConnection(_ident, isReadOnly);
         } catch (PersistenceException pe) {
-            throw new DatabaseException(pe.getMessage(), pe.getCause());
+            throw new DatabaseException("Failed get connection [ident=" + _ident +
+                                        ", isRO=" + isReadOnly + "]", pe.getCause());
         }
 
         // wrap the connection in a proxy that will collect all opened statements