move password cache into libstrophe

The cache is stored per connection object and is cleared on
* entry of wrong password
* release of connection object
* successful connection

It can be configured that libstrophe retries the password entry in case
the user entered a wrong password.

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

src/common.h

@@ -194,6 +194,12 @@ struct _xmpp_conn_t {
     xmpp_certfail_handler certfail_handler;
     xmpp_password_callback password_callback;
     void *password_callback_userdata;
+    struct {
+        char pass[1024];
+        unsigned char fname_hash[XMPP_SHA1_DIGEST_SIZE];
+        size_t passlen, fnamelen;
+    } password_cache;
+    unsigned int password_retries;
 
     /* if server returns <bind/> or <session/> we must do them */
     int bind_required;