debugdeltachain: distinct between snapshot and "other" diffs

Snapshot are expected to be healthy behavior, while "other" is a bit more
suspicious. So we distinct between the two to make it easier to inspect
repositories.

mercurial/debugcommands.py

@@ -805,10 +805,12 b' def debugdeltachain(ui, repo, file_=None'
                 deltatype = b'p1'
             elif e[3] == e[6]:
                 deltatype = b'p2'
+            elif e[3] == rev:
+                deltatype = b'base'
+            elif r.issnapshot(rev):
+                deltatype = b'snap'
             elif e[3] == rev - 1:
                 deltatype = b'prev'
-            elif e[3] == rev:
-                deltatype = b'base'
             else:
                 deltatype = b'other'
         else:

tests/test-upgrade-repo.t

@@ -1456,7 +1456,7 b' repository config is taken in account'
       rev  chain# chainlen     prev   delta       size    rawsize  chainsize     ratio   lindist extradist extraratio   readsize largestblk rddensity srchunks
         0       1        1       -1    base         77        182         77   0.42308        77         0    0.00000         77         77   1.00000        1
         1       1        2        0      p1         21        191         98   0.51309        98         0    0.00000         98         98   1.00000        1
-        2       1        2        0   other         30        200        107   0.53500       128        21    0.19626        128        128   0.83594        1
+        2       1        2        0    snap         30        200        107   0.53500       128        21    0.19626        128        128   0.83594        1
 
   $ hg debugupgraderepo --run --optimize 're-delta-all'
   upgrade will perform the following actions: