strip: compress bundle2 backup using BZ

Storing uncompressed bundle on disk would be a regression. Strip backup using
bundle2 are now compressed when requested.

mercurial/repair.py

@@ -38,13 +38,17 b' def _bundle(repo, bases, heads, node, su'
     totalhash = util.sha1(''.join(allhashes)).hexdigest()
     name = "%s/%s-%s-%s.hg" % (backupdir, short(node), totalhash[:8], suffix)
 
+    comp = None
     if cgversion != '01':
         bundletype = "HG20"
+        if compress:
+            comp = 'BZ'
     elif compress:
         bundletype = "HG10BZ"
     else:
         bundletype = "HG10UN"
-    return changegroup.writebundle(repo.ui, cg, name, bundletype, vfs)
+    return changegroup.writebundle(repo.ui, cg, name, bundletype, vfs,
+                                   compression=comp)
 
 def _collectfiles(repo, striprev):
     """find out the filelogs affected by the strip"""

tests/test-generaldelta.t

@@ -107,7 +107,7 b' Test that strip bundle use bundle2'
   0 files updated, 0 files merged, 5 files removed, 0 files unresolved
   saved backup bundle to $TESTTMP/aggressive/.hg/strip-backup/1c5d4dc9a8b8-6c68e60c-backup.hg (glob)
   $ hg debugbundle .hg/strip-backup/*
-  Stream params: {}
+  Stream params: {'Compression': 'BZ'}
   changegroup -- "{'version': '02'}"
       1c5d4dc9a8b8d6e1750966d343e94db665e7a1e9