Push back the entire 6.2 release cycle by about four weeks. In part
this slippage was caused by slippage in 6.1-RELEASE. There are
several issues that need to be resolved before we can really get the
ball rolling on 6.2; this schedule change represents our best estimate
of a realistic start and end to the 6.2 release cycle. Further
changes (as well as a more detailed 6.2 schedule) as we get closer to
the start of RELENG_6 code freeze.

While here, make the 6.3 dates "TBA" (to be announced).

Approved by: re (implicitly)
Discussed with: kensmith