Fix handling of connection pool allocation and enlargement

Fix handling of connection pool allocation and enlargement

The daemon only enlarged its connection pool when accepting new client
connections, not when establishing new outgoing server links.

Thanks to Lukas Braun (k00mi) for reporting this!

In addition this patch streamlines the connection pool allocation, so
that there is only one place in the code allocating the pool: the now
updated Socket2Index() function. The name doesn't quite fit, but this
existing and today quite useless function (because the mapping from
socket number to connection index is 1:1 today) already became called
in almost all relevant code paths, so I decided to reuse it to keep the
patch small ...probably we want to fix the naming in a second patch?

Closes #231.