Proposed 1.9 release schedule

[Bryce Harrington]

We're coming up to our next scheduled release.  I've got a few scattered
events and holidays but looking at my calendar, these dates look
feasible and fit the timeframe we wanted:

* 8/14 (Friday) - 1.8.91 (1.9 alpha)

* 9/01 (Tuesday) - 1.8.92 (1.9 beta)
    + Feature freeze

* 9/15 (Tuesday) - 1.8.93 (1.9 rc1)
    + Final freeze

* rc2 only if necessary

* 9/22 (Tuesday) - 1.9.0 (1.9 release)
    + Re-open trunk for 1.10 development

Notably, I'd like to shift from doing releases on Fridays to mid-week,
but that's mostly just for my own convenience.  If anyone prefers
strongly that I stick with Friday releases let me know.

I'm also shifting to calling the releases alpha/beta/rc instead of
alpha/rc1/rc2, since we don't typically consider that second one to be
an actual candidate for releasing.  Again, I'm guessing no one but me
cares, but if anyone wants to stick with the old approach let me know.

Bryce