convert: replace cache of (m,a,r) by (ma,r)

The next commit will rewrite the way we find changes between two
manifests. By making the cache not care about the difference between
added and modified files, we don't require the rewritten code to care
about that difference either. Also extract the call to ctx.status() to
simplify the next commit.

hgext/convert/hg.py

@@ -507,6 +507,10 b' class mercurial_source(converter_source)'
         except error.LookupError:
             return None, None
 
+    def _changedfiles(self, ctx1, ctx2):
+        m, a, r = ctx1.status(ctx2)[:3]
+        return (m + a, r)
+
     def getchanges(self, rev, full):
         ctx = self._changectx(rev)
         parents = self._parents(ctx)
@@ -514,12 +518,12 b' class mercurial_source(converter_source)'
             files = copyfiles = ctx.manifest()
         if parents:
             if self._changescache[0] == rev:
-                m, a, r = self._changescache[1]
+                ma, r = self._changescache[1]
             else:
-                m, a, r = self.repo.status(parents[0].node(), ctx.node())[:3]
+                ma, r = self._changedfiles(parents[0], ctx)
             if not full:
-                files = m + a + r
-            copyfiles = m + a
+                files = ma + r
+            copyfiles = ma
         # _getcopies() is also run for roots and before filtering so missing
         # revlogs are detected early
         copies = self._getcopies(ctx, parents, copyfiles)
@@ -582,16 +586,16 b' class mercurial_source(converter_source)'
         parents = self._parents(ctx)
         if not parents and i is None:
             i = 0
-            changes = [], ctx.manifest().keys(), []
+            ma, r = ctx.manifest().keys(), []
         else:
             i = i or 0
-            changes = self.repo.status(parents[i].node(), ctx.node())[:3]
-        changes = [[f for f in l if f not in self.ignored] for l in changes]
+            ma, r = self._changedfiles(parents[i], ctx)
+        ma, r = [[f for f in l if f not in self.ignored] for l in (ma, r)]
 
         if i == 0:
-            self._changescache = (rev, changes)
+            self._changescache = (rev, (ma, r))
 
-        return changes[0] + changes[1] + changes[2]
+        return ma + r
 
     def converted(self, rev, destrev):
         if self.convertfp is None: