Backport of 1.31-1.34:

Backport of 1.31-1.34:
- Added a downloader using urllib2 in stead of curl, based on code
donated by Kevin Ollivier. This is now the default downloader.
- Added a watcher mechanism, whereby downloaders and unpackers (and,
later builders) can give status feedback to the user. When running
pimp as a command line tool in verbose mode print this output.
- Force option should be applied to a single package, not recursively
to its dependencies. Fixes #733819.
- Don't use "dict" as a variable, it shadows the builtin. Spotted by
Bob Ippolito.
Two issues spotted by Ronald OUssoren:
- there were no accessor functions for the global per-database fields
- packages and their dependencies were installed in order in stead
  of in reverse order.