transactions: change backupfiles format to use newlines stable

transactions: change backupfiles format to use newlines

Previously the journal.backupfiles file was delimited by \0. Now we delimit it
using \n (same as the journal file). This allows us to change the number of
values in each line more easily, rather than relying on the count of \0's.

--- a/mercurial/transaction.py	Tue Oct 21 11:37:29 2014 -0700
+++ b/mercurial/transaction.py	Tue Oct 21 12:38:28 2014 -0700
@@ -128,7 +128,7 @@
         self.file.write(d)
         self.file.flush()
 
-        d = ''.join(['%s\0%s\0' % (f, b) for f, b in backups])
+        d = ''.join(['%s\0%s\n' % (f, b) for f, b in backups])
         self.backupsfile.write(d)
         self.backupsfile.flush()
 
@@ -177,7 +177,7 @@
 
         self.backupentries.append((file, backupfile, None))
         self.backupmap[file] = len(self.backupentries) - 1
-        self.backupsfile.write("%s\0%s\0" % (file, backupfile))
+        self.backupsfile.write("%s\0%s\n" % (file, backupfile))
         self.backupsfile.flush()
 
     @active
@@ -349,20 +349,16 @@
     backupjournal = "%s.backupfiles" % file
     if opener.exists(backupjournal):
         fp = opener.open(backupjournal)
-        data = fp.read()
-        if len(data) > 0:
-            ver = version
-            versionend = data.find('\n')
-            if versionend != -1:
-                ver = data[:versionend]
-                data = data[versionend + 1:]
-
+        lines = fp.readlines()
+        if lines:
+            ver = lines[0][:-1]
             if ver == str(version):
-                parts = data.split('\0')
-                # Skip the final part, since it's just a trailing empty space
-                for i in xrange(0, len(parts) - 1, 2):
-                    f, b = parts[i:i + 2]
-                    backupentries.append((f, b, None))
+                for line in lines[1:]:
+                    if line:
+                        # Shave off the trailing newline
+                        line = line[:-1]
+                        f, b = line.split('\0')
+                        backupentries.append((f, b, None))
             else:
                 report(_("journal was created by a newer version of "
                          "Mercurial"))