setup: use sys.executable to call hg
Executing ".\hg" does not work on Windows, but we can instead ask
Python to execute hg.
adding file
% create a second head
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
created new head
% failing merge
0 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges
% resolve -l, should be empty