repair: mark the critical section of strip() as unsafe

When our experimental nointerrupt feature is enabled, this will
help prevent users from corrupting their repo during a strip.

Differential Revision: https://phab.mercurial-scm.org/D3717

mercurial/repair.py

@@ -186,6 +186,7 def strip(ui, repo, nodelist, backup=Tru
         tmpbundlefile = backupbundle(repo, savebases, saveheads, node, 'temp',
                                      compress=False, obsolescence=False)
 
+    with ui.uninterruptable():
     try:
         with repo.transaction("strip") as tr:
             offset = len(tr.entries)