changegroup: add "vfs" argument to "writebundle()" for relative access via vfs

Before this patch, filename specified to "changegroup.writebundle()"
should be absolute one.

In some cases, they should be relative to repository root, store and
so on (backup before strip, for example).

This patch adds "vfs" argument to "writebundle()", and makes
"writebundle()" open (and unlink) "filename" via vfs for relative
access, if both filename and vfs are specified.

mercurial/changegroup.py

@@ -59,7 +59,7 b' bundletypes = {'
 # hgweb uses this list to communicate its preferred type
 bundlepriority = ['HG10GZ', 'HG10BZ', 'HG10UN']
 
-def writebundle(cg, filename, bundletype):
+def writebundle(cg, filename, bundletype, vfs=None):
     """Write a bundle file and return its filename.
 
     Existing files will not be overwritten.
@@ -72,6 +72,9 b' def writebundle(cg, filename, bundletype'
     cleanup = None
     try:
         if filename:
+            if vfs:
+                fh = vfs.open(filename, "wb")
+            else:
             fh = open(filename, "wb")
         else:
             fd, filename = tempfile.mkstemp(prefix="hg-bundle-", suffix=".hg")
@@ -112,6 +115,9 b' def writebundle(cg, filename, bundletype'
         if fh is not None:
             fh.close()
         if cleanup is not None:
+            if filename and vfs:
+                vfs.unlink(cleanup)
+            else:
             os.unlink(cleanup)
 
 def decompressor(fh, alg):