Adding flexibility to dhcpd (code submitted)

[tallynerdy]

Hi Folks,
I've done a little work in getting more flexibility into the DHCPD configuration of pfsense. I've only gone as far as allowing static mappings on ipalias subnets in my submission, but have some code which also allows for creation of ipalias subnet ranges. The reason I haven't released that bit is because of how complicated it gets to validate the new ranges within the existing codebase without a big refactor. Please have a look and let me know what you think.

Cheers!
Colin

This is my pull request to RELENG_2_3_4 with the changes:
https://github.com/pfsense/pfsense/pull/3836