obsstore: record data as floating point in fm0 format

For python struct module, "d" is double. But for python string
formating, "d" is integer. We want to preserve the floating point
nature of the data, so we store it in the metadata as floating
point. We use "%r" to make sure we get as many significant digitis as
necessary to restore the float to the exact same value on the other
side.

The fm1 is transmitting the information as float. The lack of this made
fm1-stored markers not survive a round-trip to fm0 leading to duplicated
markers (or two markers very alike).

mercurial/obsolete.py

@@ -202,7 +202,8 b' def _fm0encodeonemarker(marker):'
     if flags & usingsha256:
         raise util.Abort(_('cannot handle sha256 with old obsstore format'))
     metadata = dict(metadata)
-    metadata['date'] = '%d %i' % date
+    time, tz = date
+    metadata['date'] = '%r %i' % (time, tz)
     if parents is not None:
         if not parents:
             # mark that we explicitly recorded no parents