[Scan-DC] another Potomac frequency

[Mike Agner]

  While programming in some Dulles freqs and scanning, I heard a controller
at Dulles say to go to 'Potomac Approach' on 123.82.  I plugged in 123.825
into another radio, and sure enough, I heard the United flight checking in-
so add this frequency to the list of Potomac TRACON freqs.

73s  Mike