jabber.c: use FREE_SET_NULL macro
refactored jabber_connect functions

* similar code moved to jabber_connect()
* variables saved_* moved to a structure saved_user
* 'user' renamed to 'jid'
set NULL only when resource != NULL in FREE_SET_NULL
fixed memory leak in jabber_subscription()
added JABBER_PRIORITY_* macros
refactored jabber_set_autoping()
room_jid should be (char *)
don't release room and nick when parsing failed
fixed resources release

* Use free instead of g_free as resources are allocated with strdup
* Fixed memory leaks
check account->name == NULL
Merge pull request #132 from pasis/next

Some code refactoring in jabber.c