Added debian/freeradius-rest to gitignore

Otherwise, building a Debian package leaves a change in the repository.
Tested with Debian Wheezy 32bit on tag release_3_0_4_rc0 and current
master (commit 73c90fc26a6a56becdf9153abce8d05175fdb06a).
Merge pull request #667 from qnet-herwin/debian_freeradius_rest

Added debian/freeradius-rest to gitignore