title: Prevent retroactive modification of database migrations between mercurial branches
body: <p>Is it possible to prevent someone from pushing commit which touches already applied (committed to separate branch) database migrations?</p>
  
  <p>For example, in default branch there are existing migrations 01 and 02 (already applied). In development branch someone adds migration 03 but also modifies migration 02. How to prevent this commit via mercurial hook?</p>