dnsmasq: misc fixes

Closes #527

* convert to Makefile.autotools.in format
* Bump to version 2.50 fixes security issues CVE 2009-2957 and 2009-2958.
* fix dbus paths and dependencies
* Install manpage conditionally
* Introduce new DHCP server option

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Daniele Salvatore Albano <d.albano@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>