D1502: rewriteutil: add utility function to check if we can create new unstable cset

[pulkit (Pulkit Goyal)]

pulkit added a comment.


  In https://phab.mercurial-scm.org/D1502#25341, @dlax wrote:
  
  > > This rewriteutil.py introduced in this patch and the utility functions added in the upcoming patches exists in the evolve extension are being ported from there.
  >
  > Is it worth porting this alone if nothing in core makes use of this module?
  >  Or is there a larger plan?
  
  
  I have updated the series with couple of usages. More functions will be introduced which will be used by both core and extensions.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D1502

To: pulkit, #hg-reviewers
Cc: dlax, mercurial-devel