Changing the way we recognize lists

Right now there is a blanding of recognizing a list and validating it.
This change introduces a new method called IsVarList(...) which
checks if a variable is a list and returns true or false. The check is
more complete than the previous check and makes sure that a list is a
proper list and not something that just contains '@'.
Fixed regex for commented lines in *_variable_values_ini
New option `--print-digest`/`-p` for `cf-key`.

With the new option it is possible to print the default CFEngine
digest value for a given public key file.
New option `--trust-key`/`-t` for `cf-key`.

This new option copies the given public key file
to the file name where `cf-serverd` would have stored
it if it had been gotten as the result of a successful
network exchange.

Such an option is intended to be used in fully-automated
installs, when there is a trusted way of deploying client
keys on the server and vice-versa.

  modified:   cf-key.c