Rearrange the git configuration slightly:

Rearrange the git configuration slightly:
 - List "pockets" instead of "branches" to divorce our pockets from
   git branches specifically.
 - Each pocket can have a "git" and/or "apt" attribute. Both default
   to the name of the pocket if unspecified.
 - Add an allow_backtracking field, which indicates whether
   non-fast-forwards are allowed and whether version numbers have to
   be monotonically increasing.

svn path=/trunk/packages/xvm-prodconfig/; revision=2514