1.30.1: conditionalize fork support on Unix. Try to fix clisp support (untested).

Also, add a README file.
1.30.2: try to fix waitpid on allegro.
1.30.3: fix an issue causing POIU to not skip effectively done actions.

The above bug was particular bad, because it would cause asdf
to spuriously be reloaded, which would interfere with poiu itself,
and cancel extensions such as cffi-grovel, etc.

Also, better fix posix-waitpid on allegro.