make sure that verbose mode is only applied once

lib/sqlite3.js

@@ -48,8 +48,11 @@ Database.prototype.each = function(sql) {
     return this;
 }
 
+var isVerbose = false;
+
 // Save the stack trace over EIO callbacks.
 sqlite3.verbose = function() {
+    if (!isVerbose) {
         var trace = require('./trace');
         trace.extendTrace(Database.prototype, 'prepare');
         trace.extendTrace(Database.prototype, 'get');
@@ -65,5 +68,8 @@ sqlite3.verbose = function() {
         trace.extendTrace(Statement.prototype, 'each');
         trace.extendTrace(Statement.prototype, 'reset');
         trace.extendTrace(Statement.prototype, 'finalize');
+        isVerbose = true;
+    }
+
     return this;
 };