This commit removes the 'megaclass' code that IPC::Pipe has become to
support two different dataflow paths in a single class.
Instead, we use up to 2 different IPC objects in async mode to give the
dataflow needed.
Splitting this up required moving the message boundary detection code
back to IPC::Pipe. It is now expected that a given IPC subclass is able
to pass messages with message boundaries intact, and to block while
waiting for messages if concurrency is supported. IPC::Null already
maintains message boundaries and doesn't support concurrency.
Previously IPC and IPC::Pipe cooperated to perform message boundary
detection, by inserting and removing '\n' characters. This was always
kind of a hack. Now we simply pass the message length across the pipe
followed by the message, and ignore the idea completely in IPC.
The impetus for all of this had been to improve performance, but
unfortunately that hasn't happened here, although it's still a positive
change from the code simplicity front.
This can be used as a run-time check later to ensure that kdesrc-build
finds compatible versions of its component modules (though that isn't
done yet).
Michael Pyne