revlog.revision(): minor cleanup

Rename some variables, making the name more obvious (in particular "cache" was
actually two different variable.
Move code around, moving the index preloading before the deltachain computation,
without that index preloading was useless (everything was read in deltachain).

mercurial/revlog.py

@@ -1056,26 +1056,30 b' class revlog(object):'
 
     def revision(self, node):
         """return an uncompressed revision of a given node"""
-        cache = nullrev
+        cachedrev = nullrev
         if node == nullid:
             return ""
         if self._cache:
-            cache = self._cache[1]
             if self._cache[0] == node:
                 return self._cache[2]
+            cachedrev = self._cache[1]
 
         # look up what we need to read
         text = None
         rev = self.rev(node)
-        cache, base, chain = self.deltachain(rev, cache)
+        base = self.base(rev)
 
         # check rev flags
         if self.flags(rev) & ~REVIDX_KNOWN_FLAGS:
             raise RevlogError(_('incompatible revision flag %x') %
                               (self.flags(rev) & ~REVIDX_KNOWN_FLAGS))
 
+        # build delta chain
+        self._loadindex(base, rev + 1)
+        cachehit, base, chain = self.deltachain(rev, cachedrev)
+
         # do we have useful data cached?
-        if cache and self._cache:
+        if cachehit and self._cache:
             global _cached
             _cached += 1
             text = self._cache[2]
@@ -1087,7 +1091,6 b' class revlog(object):'
         # drop cache to save memory
         self._cache = None
 
-        self._loadindex(base, rev + 1)
         self._chunkraw(base, rev)
         if text is None:
             text = self._chunk(base)