unshelve: disable unshelve during merge (issue5123) As stated in the issue5123, unshelve can destroy the second parent of the context when tried to unshelve with an uncommitted merge. This patch makes unshelve to abort when called with an uncommitted merge. See how shelve.mergefiles works. Commit structure looks like this: ``` ... -> pctx -> tmpwctx -> shelvectx / / second merge parent pctx = parent before merging working context(first merge parent) tmpwctx = commited working directory after merge(with two parents) shelvectx = shelved context ``` shelve.mergefiles first updates to pctx then it reverts shelvectx to pctx with: ``` cmdutil.revert(ui, repo, shelvectx, repo.dirstate.parents(), *pathtofiles(repo, files), **{'no_backup': True}) ``` Reverting tmpwctx files that were merged from second parent to pctx makes them added because they are not in pctx. Changing this revert operation is crucial to restore parents after unshelve. This is a complicated issue as this is not fixing a regression. Thus, for the time being, unshelve during an uncommitted merge can be aborted. (Details taken from http://mercurial.808500.n3.nabble.com/PATCH-V3-shelve-restore-parents-after-unshelve-issue5123-tt4036858.html#a4037408) Differential Revision: https://phab.mercurial-scm.org/D6169