import: show the warning message for failure of merging Before this patch, no message is shown for failure of merging at "hg import". In such case, merging patch is imported as a normal revision silently, and it may confuse users. For simplicity, this patch recommends just using "--exact", even though importing the merging patch itself is possible without it if: - the hash of the 1st parent in the patch is equal to one of the patch imported just before (or the parent of the working directory, for the 1st patch of the series), and - the hash of the 2nd parent in the patch is known in the local repository