smartlog: be graceful when ancestorcache db is corrupted

Summary:
We have seem some errors when closing the database during `db.close()`. This
diff nukes the database if that happens.

Test Plan: arc unit

Reviewers: #mercurial, mjpieters

Reviewed By: mjpieters

Subscribers: medson, mjpieters

Differential Revision: https://phabricator.intern.facebook.com/D5305123

Signature: t1:5305123:1498166056:8355e861c18c670e6342e541f2bc55d65bc7b1c8

hgext3rd/smartlog.py

@@ -86,7 +86,11 @@ def ancestorcache(path):
             yield
         finally:
             extensions.unwrapfunction(revlog.revlog, 'ancestor', revlogancestor)
-            db.close()
+            try:
+                db.close()
+            except Exception:
+                # database corruption, we just nuke the database
+                util.tryunlink(path)
 
 def _drawendinglines(orig, lines, extra, edgemap, seen):
     # if we are going to have only one single column, draw the missing '|'s