Fix another variable capture bug in pattern compilation
Fix another variable capture bug in pattern compilation

- When patterns are split, variables from the first row get substituted
  into the latter ones because the new scrutinees use variables from the
  first row. However, this was not taking into account that the same
  user variable could be used for different things in each row.
- Fixed by just making up fresh variables for every pattern, and
  replacing the user-provided variables.

unisonweb/platform,unisonweb/platform,unisonweb/platform