This is an alternative to HostileFork's "notorious TCP bug fix"

(EVM_DEVICE events allowing ports to be collected) minimized. It is meant as an alternative to the pull request #158 .
Tested under Linux (0.4.4) with no regressions.

Differences:

- keeps marking code in the garbage collector sources
- no need for special tests whether parts of the GC are called from inappropriate places
- not making changes unrelated to the problem
- traverses the list of requests