* Support SNMPv3
* Default SNMP version is 2c
* Use newer Grecs
* Drop unneeded dependencies
* Variable assignments in expressions
* Detection of SNMP counter overflows
* Comma operator
* Support for indexed MIBs

This feature allows you to use symbolic names instead of the fixed MIBs
for MIBs that are part of SNMP subtrees.  For example, to get number of
packets sent over eth0 into variable "out", you would do the following:

    table iftable IF-MIB::ifDescr;
    variable out "IF-MIB::ifOutUcastPkts.$iftable[eth1]";

The first statement converts the subtree into a "table" named "iftable".
The second statement references an entry in this table that has
the value "eth1".  For example, if the SNMP tree has the following MIB

    IF-MIB::ifDescr.10: eth0

then the expression "$iftable[eth]" yields "10"

* Assertion syntax changed.

The assertion statement takes a single argument, which must be a
string consisting of the following three parts:

   <oid: string> [!]<opcode>[/i] <value: string>

The <opcode> part can be either an arithmetical operator (=, <, <=, >,
>=), or any of the following string operators:

    eq          string equality
    ne          string inequality
    prefix      oid value must begin with <value>
    suffix      oid value must end with <value>
    glob        <value> is a glob(7) pattern that oid value must match

Each of these can be suffixed with "/i" to request case-insensitive comparison.

A "!" in front of opcode reverts its meaning.

The <value> part must not include the type prefix.