"Applet" is a much better name for the external command-line
scripts and programs that can be loaded as PBot commands. They
will no longer be confused with Perl modules.
https://en.wikipedia.org/wiki/Applet
If ProcessManager::execute_process() returns undef,
then the loop in Interpreter::interpret() thinks that
the command didn't get handled, and so goes on to look
for other commands. This is now corrected.
