SocketManager: convert impossible warning to AIM_DIE
SocketManager: standardize on AIM_LOG_* logging macros
SocketManager: move most ERROR logs to INTERNAL

I think all of these could actually be assertions, but that would be too risky
for now.
SocketManager: tweak loglevels
SocketManager: cleanup log message when exceeding maximum timers
SocketManager: use aim_main in utest

This fixes registering the log structs so we can turn on trace logging during
the utest.
SocketManager: fix bug in timer utest

This assertion expects exactly one of the timers to fail to unregister.
Previously if the first timer failed to be unregistered then the OR would
short-circuit and the second unregistration would not occur. Replacing the OR
with XOR ensures no short circuiting and checks that exactly one unregister
failed.
Merge into master from pull request #167:
SocketManager log cleanup (https://github.com/floodlight/indigo/pull/167)