configure: set version to 0.2.1-pre
Revert "options: add a secret command line option"

This reverts commit fee03d46ddc0f47083f87888d3411f1465aa74da.

Removing this as it is temporary and for version 0.2.0 only.
libcommon: fix a debug compile warning
libmemdisc: fix stage 0 and enhance error handling

In stage 0 we only want to see heap start and stack end.
Afterwards, stop all activity different from libc behavior. But
we've seen that there are output FIFO flushes and further debug
information. So skip these steps completely.
Close all FIFOs and the debug log in case an error occurs or stage
0 is configured.
Also close the input FIFO after running the constructor as it is
not required any more afterwards.