Helper thread for module source
===============================

init.c
------

OutputBufferFlush(0) now does a fwritePar instead of fwrite.
fwritePar hands over to fwrite directly, if the global temporary
buffer TWdata has not been allocated, and otherwise copies data
to that buffer, waits for a mutex, and lets a freshly created
thread do the fwrite.
The last call to OutputBufferFlush(1) in cleanup makes sure that the helper
thread has finished, and does a normal fwrite.
TWdata will be allocated, when setDetachedWrite() from init.c is 
called once in a module's main, like
if (NThreads > 0)
    setDetachedWrite();
in source.c
