Does the login on the FTP server you are connected to. for that you first have
to connect to a FTP server before logging in. Username and Password can either be
set by the parameters or manually before (using the set-methods).
Parameter
string $username = null - The username
to be used for login to. This parameter can be left out, if it has been set manually!
int $password = null - The password to use for
login. This parameter can be left out, if it has been set manually!
Return value
mixed - true on success, otherwise PEAR::Error.
Throws
The returned PEAR_Error object in case of an error
is unspecific. You can ignore the errornumber and errormessage,
because only "Login failed" will be returned if the
login fails.
