Description:
------------
snmprealwalk with non numeric object_id resets oid output format for current call, and future calls.

Test script:
---------------
<?php
snmp_set_oid_output_format(SNMP_OID_OUTPUT_NUMERIC);
print_r(snmprealwalk('1.2.3.4', 'public', '.1.3.6.1.2.1.17.2.15.1.3.1'));
print_r(snmprealwalk('1.2.3.4', 'public', 'BRIDGE-MIB::dot1dStpPortState.1'));
print_r(snmprealwalk('1.2.3.4', 'public', '.1.3.6.1.2.1.17.2.15.1.3.1'));
?>

Expected result:
----------------
Array
(
    [.1.3.6.1.2.1.17.2.15.1.3.1] => INTEGER: 5
)
Array
(
    [.1.3.6.1.2.1.17.2.15.1.3.1] => INTEGER: 5
)
Array
(
    [.1.3.6.1.2.1.17.2.15.1.3.1] => INTEGER: 5
)

Actual result:
--------------
Array
(
    [.1.3.6.1.2.1.17.2.15.1.3.1] => INTEGER: 5
)
Array
(
    [.1.3.6.1.2.1.17.2.15.1.3.1] => INTEGER: forwarding(5)
)
Array
(
    [.1.3.6.1.2.1.17.2.15.1.3.1] => INTEGER: forwarding(5)
)