Add limit param to split_command_parts(), fix twitter quotes bug

Only took me a few months to write. I even added a test case.
Fix the NSS init after fork bug, and clean up lies in unix.c

This might look like a simple diff, but those 'lies' made this not very
straightforward.

The NSS bug itself is simple: NSS detects a fork happened after the
initialization, and refuses to work because shared CSPRNG state is bad.
The bug has been around for long time. I've been aware of it for 5
months, which says something about this mess. Trac link:

http://bugs.bitlbee.org/bitlbee/ticket/785

This wasn't a big deal because the main users of NSS (redhat) already
applied a different patch in their packages that workarounded the issue
somewhat accidentally. And this is the ticket for the 'lies' in unix.c:

http://bugs.bitlbee.org/bitlbee/ticket/1159

Basically a conflict with libotr that doesn't happen anymore. Read that
ticket for details on why ignoring those comments is acceptable.

Anyway: yay!