Disentangle listener and connection, allowing the struct definitions to move

Disentangle listener and connection, allowing the struct definitions to move
out of the headers into the code, reducing header dependencies.
Add code to detect the number of CPU cores on Linux.
Fork as many listening child processes as we have CPU cores.
Add timestamps and the current PID to log messages.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@6 d4fa192b-c00b-0410-8231-f00ffab90ce4