Metacello 1.0-beta.28.2 released

...partially. SqueakSource is down, so the release is only to the
GemSource repository at this time.

features/fixes:

  - add #''pharo1.3.x'' attribute
  - get rid of #sortBy: ... deprecated in Pharo1.2

Tests run clean in Pharo1.2 #12320...

Dale