Issue 209 - support drop/modified conflict (monotone)

Hello,

A new issue has been created:

209 - support drop/modified conflict
Project: monotone
Status: New
Reported by: Stephen Leake
Labels:
 Type:Incorrect Behavior
 Priority:Medium

Description:

Steps to reproduce the problem:
-------------------------------

1. create two heads, one with file_a modified, one with file_a dropped
2. merge

Expected result:
----------------
merge reports a drop/modified conflict

Actual results:
---------------
warning about modifications being lost due to drop

Output of `mtn version --full`:
-------------------------------
1.0

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Issue: https://code.monotone.ca/p/monotone/issues/209/