GitLab

* New packages format lets you select source control system in use
* Packages file now includes root repo explicitly
* Scripts darcs-all and push-all updated for the new packages format only
* New sync-all script, intended for use after Git changeover and for buildbots right now
* Had to remove libraries/bootstrapping from tree since Git cannot track empty directories without a hack
* Determine checkout date with Git using Darcs fallback in aclocal.m4

The flag is off by default, but GHCi turns it on (in Main.hs).  For
GHCi it can be overriden on the command-line or using :set.

GHC 6.9+ can properly handle cross-package recompilation checking, but
older versions of GHC couldn't, so in stage1 we always rebuild
Main.hs.  In other words, 'make' in ghc/ should do the right thing now.