It seems that the distributions places nologin in different
places (e.g. deb based distribution in /usr/sbin, rpm based and gentoo
in /sbin).  This patch fixes this behaviour searching for nologin in
the PATH environment variable.

Now a variable for the SPOOL_DIR is been allocated.

Now a variable is used for the spool file and the installation process
is less verbose.

As for the PostInstall script, the Uninstall script must be
adapted to the new username (_cado)

The getopt_long descriptors was not correctly terminated.
To avoid a segmentation fault the list should be terminated
by an array composed of 4 NULLs.

PostInstall was refactored to mimick the debian installer.

PostInstall check, removed unused retvalue warnings, config.h patch

CMake conversion

cadrop permits to drop ambient capabilities.

With this fix /proc/<pid>/cmdline is preserved.

users cannot use symlinks when editing the scado file.

Like
$ EDITOR="vim -i 'startinsert'" scado -e
or
$ EDITOR="cp saved_scado_file" scado -e

add checks for libcap and PAM headers