resolve: abort when not applicable (BC)
The resolve command is only relevant when mergestate is present.
This patch will make resolve abort when no mergestate is present.
This change will let people know when they are using resolve when they
shouldn't be. This change will let people know when their use of resolve
doesn't do anything.
Previously, |hg resolve -m| would allow mergestate to be created. This
patch now forbids that. Strictly speaking, this is backwards
incompatible. The author of this patch believes creating mergestate via
resolve doesn't make much sense and this side-effect was unintended.