record: check that we are not committing a merge before patch selection
It might sound like a good idea to use record to filter changes when merging.
If someone attemps this, it's better to tell her "no" right ahead, before the
patch generation/line selection, so she does not spend time doing it just to
receive a red light after that (sometimes rather long) process.
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 or 'hg update -C' to abandon
% resolve -l, should be empty