small improvements + configurable DNSDomain

- fixed handling of expiry
- fixed calculation of expiry period
- reduced CNAME checks / lookups to when really needed

dyndns.cfg.dist

@@ -6,6 +6,14 @@
 # DNS Settings
 #dns_server = 192.168.1.1       # DNS Server to communicate with (use IP!)
 
+dns_domain = ?, !, 1 		# DNS Domain to support, match hostname with:
+				# '?' - take domain name from parameter 'domain'
+				# '!' - take domain name from virtualhost name
+				# positive number - last # parts from hostname
+				# negative number - last # parts from virtualhost
+				# any other string - use if hostname ends on this
+
+
 #expand_cnames = 1              # CNAME levels to expand (0 to disable)
 #require_rr =		        # Require existing record of this type to update
 #replace_rr = A, AAAA, TXT	# Records types to replace (clear) during update