Add a parameter to generate-working-copy-states.py that indicates
how many changesets are wanted. This number impacts all the
subcommands. The current 'filelist' subcommand becomes 'filelist 2',
the current 'base' and 'parent' subcommands become 'state 2 1' and
'state 2 2' respectively, while 'wc' becomes 'state 2 wc'.
See earlier patch for motivation.
The script can currently generate filenames and contents for exactly
two changesets plus the working copy. For some tests (e.g. of plain
dirstate status), only one changeset is needed, while for others
(e.g. merge), three changesets are needed. Let's prepare for such
tests by generalizing the code for any number of changesets.
