Make stopping the manager (the entire manager sup tree)
more easy. The function(s) for starting and stopping the
manager that exist in the snmpm module is (mostly) intended
for testing, making the stop function more "potent" is no
real problem (now any process not just the parent) can stop
the manager process tree.

The function 'snmp:print_version_info/0' which prints
various (version) info, attempted to extract the
"compile time" of each module in the snmp app.
This info used to be availabe in the module_info of
each module, but has been removed (a "long" time ago).
This resulted in a pointless "Not Found" beeing printed.
This has now been removed from the into printed.

OTP-15330

OTP-15932

Warning for some functions "for no reason" (obviously
there is a reason, but I have to dig deeeep to find it).
Also warnings for stuff there is no way to type today
(for instance, improper lists).

OTP-15932

Changes to satisfy dialyzer. Including changing the definition
of some of the behaviours (use the '-callback' attribute instead
of an explicit behaviour_info/1 function).

Also found and corrected some (apparently minor) bugs.

OTP-15932

Changes to satisfy dialyzer. Including changing the definition
of the snmpm_network_interface behaviour (use the '-callback'
attribute instead of an explicit behaviour_info/1 function).

OTP-15932

Make target (for running dialyzer on snmp), os usage
and a minor snmp_log ("future proofing").

OTP-15932