Downgrade the XMPP "network connection failed" exception from error to info. SC reports

this problem using a message window. Also frame the logger.info call with logger.isInfoEnabled
to avoid overhead to build the info message.

src/net/java/sip/communicator/impl/gui/main/login/LoginManager.java

@@ -449,8 +449,11 @@ private void handleOperationFailedException(OperationFailedException ex)
                 break;
             case OperationFailedException.NETWORK_FAILURE:
             {
-                logger.error("Provider could not be registered"
-                    + " due to a network failure: " + ex);
+                if (logger.isInfoEnabled())
+                {
+                    logger.info("Provider could not be registered"
+                            + " due to a network failure: " + ex);
+                }
 
                 AccountID accountID = protocolProvider.getAccountID();
                 errorMessage = GuiActivator.getResources().getI18NString(

src/net/java/sip/communicator/impl/protocol/jabber/ProtocolProviderServiceJabberImpl.java

@@ -348,8 +348,11 @@ private synchronized void connectAndLogin(SecurityAuthority authority,
                 }
                 catch (XMPPException exc)
                 {
-                    logger.error("Failed to establish a Jabber connection for "
-                        + getAccountID().getAccountUniqueID(), exc);
+                    if (logger.isInfoEnabled()) 
+                    {
+                        logger.info("Failed to establish a Jabber connection for "
+                                + getAccountID().getAccountUniqueID(), exc);
+                    }
 
                     throw new OperationFailedException(
                         "Failed to establish a Jabber connection for "