Drop release times for CNode
Drop release times for CNode

It seems there were two mechanisms for assessing whether a CNode
was still in use: a refcount and a release timestamp. The latter
seems to have been there for a long time, as a safety mechanism.

However, this timer also keeps CNode objects alive for far longer
than necessary after disconnects, potentially opening up a DoS
window.

This commit removes the timestamp-based mechanism, and replaces
it with an assert(nRefCount >= 0), to verify that the refcounting
is indeed correctly working.

Conflicts:
	src/net.h

Jheguy2/Mercury,Jheguy2/Mercury,Jheguy2/Mercury,robvanmieghem/clams,thunderrabbit/clams,nochowderforyou/clams,Kefkius/clams,Kefkius/clams,robvanmieghem/clams,Kefkius/clams,Jheguy2/Mercury,nochowderforyou/clams,Kefkius/clams,nochowderforyou/clams,nochowderforyou/clams,dooglus/clams,thunderrabbit/clams,thunderrabbit/clams,thunderrabbit/clams,thunderrabbit/clams,dooglus/clams,robvanmieghem/clams,dooglus/clams,robvanmieghem/clams,dooglus/clams,Jheguy2/Mercury,robvanmieghem/clams,dooglus/clams,Kefkius/clams,nochowderforyou/clams