largefiles: walk history in ascending order while downloading all lfiles

I don't think the order matters. Maybe it's purely because of the use of
walkchangerevs(), which was originally designed for "hg log" command.

Surprisingly, the number of objects fetched in test-largefiles.t has changed.
According to the --verbose output, the order of the following fetches flipped
and the latter got deduplicated.

  getting large3:eb7338044dc27f9bc59b8dd5a246b065ead7a9c4
  found eb7338044dc27f9bc59b8dd5a246b065ead7a9c4 in store
  getting sub/large4:eb7338044dc27f9bc59b8dd5a246b065ead7a9c4
  found eb7338044dc27f9bc59b8dd5a246b065ead7a9c4 in store

hgext/largefiles/lfcommands.py

@@ -489,7 +489,7 b' def downloadlfiles(ui, repo):'
     tonode = repo.changelog.node
     totalsuccess = 0
     totalmissing = 0
-    for rev in repo.revs(b'reverse(file(%s))', b'path:' + lfutil.shortname):
+    for rev in repo.revs(b'file(%s)', b'path:' + lfutil.shortname):
         success, missing = cachelfiles(ui, repo, tonode(rev))
         totalsuccess += len(success)
         totalmissing += len(missing)

tests/test-largefiles.t

@@ -1005,7 +1005,7 b' Test cloning with --all-largefiles flag'
   getting changed largefiles
   3 largefiles updated, 0 removed
   5 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  8 additional largefiles cached
+  7 additional largefiles cached
 
   $ rm "${USERCACHE}"/*
   $ hg clone --all-largefiles -u 0 a a-clone0
@@ -1013,7 +1013,7 b' Test cloning with --all-largefiles flag'
   getting changed largefiles
   2 largefiles updated, 0 removed
   4 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  9 additional largefiles cached
+  8 additional largefiles cached
   $ hg -R a-clone0 sum
   parent: 0:30d30fe6a5be 
    add files
@@ -1047,7 +1047,7 b' Test cloning with --all-largefiles flag'
 
   $ rm "${USERCACHE}"/*
   $ hg clone --all-largefiles -U a a-clone-u
-  11 additional largefiles cached
+  10 additional largefiles cached
   $ hg -R a-clone-u sum
   parent: -1:000000000000  (no revision checked out)
   branch: default

tests/test-lfconvert.t

@@ -389,17 +389,17 b' Ensure the abort message is useful if a '
   $ rm largefiles-repo/.hg/largefiles/*
   $ hg lfconvert --to-normal issue3519 normalized3519
   initializing destination normalized3519
-  anotherlarge: largefile 3b71f43ff30f4b15b5cd85dd9e95ebc7e84eb5a3 not available from file:/*/$TESTTMP/largefiles-repo (glob)
-  stuff/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
-  stuff/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
-  sub/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
+  large: largefile 2e000fa7e85759c7f4c254d4d9c33ef481e459a7 not available from file:/*/$TESTTMP/largefiles-repo (glob)
   large: largefile 2e000fa7e85759c7f4c254d4d9c33ef481e459a7 not available from file:/*/$TESTTMP/largefiles-repo (glob)
-  sub/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
+  sub/maybelarge.dat: largefile 34e163be8e43c5631d8b92e9c43ab0bf0fa62b9c not available from file:/*/$TESTTMP/largefiles-repo (glob)
   large: largefile 2e000fa7e85759c7f4c254d4d9c33ef481e459a7 not available from file:/*/$TESTTMP/largefiles-repo (glob)
   stuff/maybelarge.dat: largefile 34e163be8e43c5631d8b92e9c43ab0bf0fa62b9c not available from file:/*/$TESTTMP/largefiles-repo (glob)
   large: largefile 2e000fa7e85759c7f4c254d4d9c33ef481e459a7 not available from file:/*/$TESTTMP/largefiles-repo (glob)
-  sub/maybelarge.dat: largefile 34e163be8e43c5631d8b92e9c43ab0bf0fa62b9c not available from file:/*/$TESTTMP/largefiles-repo (glob)
-  large: largefile 2e000fa7e85759c7f4c254d4d9c33ef481e459a7 not available from file:/*/$TESTTMP/largefiles-repo (glob)
+  sub/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
+  sub/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
+  stuff/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
+  anotherlarge: largefile 3b71f43ff30f4b15b5cd85dd9e95ebc7e84eb5a3 not available from file:/*/$TESTTMP/largefiles-repo (glob)
+  stuff/maybelarge.dat: largefile 76236b6a2c6102826c61af4297dd738fb3b1de38 not available from file:/*/$TESTTMP/largefiles-repo (glob)
   0 additional largefiles cached
   11 largefiles failed to download
   abort: all largefiles must be present locally