add blurbs for recent release candidates

Changes in version 0.2.1.17-rc - 2009-07-07

  Tor 0.2.1.17-rc marks the fourth -- and hopefully last -- release

  candidate for the 0.2.1.x series. It lays the groundwork for further

  client performance improvements, and also fixes a big bug with directory

  authorities that were causing them to assign Guard and Stable flags

  poorly.

  The Windows bundles also finally include the geoip database that we

  thought we'd been shipping since 0.2.0.x (oops), and the OS X bundles

  should actually install Torbutton rather than giving you a cryptic

  failure message (oops).

  o Major features:

    - Clients now use the bandwidth values in the consensus, rather than

      the bandwidth values in each relay descriptor. This approach opens

Changes in version 0.2.1.16-rc - 2009-06-20

  Tor 0.2.1.16-rc speeds up performance for fast exit relays, and fixes

  a bunch of minor bugs.

  o Security fixes:

    - Fix an edge case where a malicious exit relay could convince a

      controller that the client's DNS question resolves to an internal IP

Changes in version 0.2.1.15-rc - 2009-05-25

  Tor 0.2.1.15-rc marks the second release candidate for the 0.2.1.x

  series. It fixes a major bug on fast exit relays, as well as a variety

  of more minor bugs.

  o Major bugfixes (on 0.2.0.x):

    - Fix a timing-dependent, allocator-dependent, DNS-related crash bug

      that would occur on some exit nodes when DNS failures and timeouts