Removing smbc_set_credentials() call from libsmbclient.

[Jeremy Allison]

I'd really like to remove smbc_set_credentials() from
libsmbclient if possible. It doesn't take a SMBCCTX *
pointer and thus depends on global variables to store
the user credentials.

Is this function actually being used anywhere external
to Samba ?

I'm trying to get libsmbclient into a thread-safe state
(slow work, I know), and this is a major blocker....

Jeremy.