dagop: extract headsetofconnecteds() from dagutil...
dagop: extract headsetofconnecteds() from dagutil
The functionality for resolving the set of DAG heads from a
subset simply requires a function to resolve parent revisions.
Let's establish a function in the dagop module to do this, which
seems to be where generic DAG functionality goes these days.
Differential Revision:
https://phab.mercurial-scm.org/D4327