general-functions.pl: Update to fix bug #12428

general-functions.pl: Update to fix bug #12428

- Patch of general-functions.pl for implementation of fix provided
	by Bernhard Bitsch in bug #12428.
	Had to be modified as that fix gave a failure for single character hostnames.
	Updated version prevents spaces being put into hostnames and works for single
	character hostnames
- Updated subroutine validfqdn to apply consistent rules for hostname & domain name
	portions of fqdn
- Minor updates for consistency across validhostname, validdomainname & validfqdn
- Patch implemented into testbed system and confirmed working for hostnames, domain names
	and FQDN's.

Signed-off-by: Adolf Belka <ahb.ipfire@gmail.com>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>