vcs.rb: checkout the current branch before rebase

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62105 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/vcs.rb

@@ -487,6 +487,7 @@ class VCS
     def commit
       rev = cmd_read(%W"#{COMMAND} svn info"+[STDERR=>[:child, :out]])[/^Last Changed Rev: (\d+)/, 1]
       com = cmd_read(%W"#{COMMAND} svn find-rev r#{rev}").chomp
+      head = cmd_read(%W"#{COMMAND} symbolic-ref --short HEAD").chomp
 
       commits = cmd_read([COMMAND, "log", "--reverse", "--format=%H %ae %ce", "#{com}..@"], "rb").split("\n")
       commits.each_with_index do |l, i|
@@ -496,6 +497,7 @@ class VCS
         dcommit << "--add-author-from" unless a == c
         dcommit << r
         system(*dcommit) or return false
+        system(COMMAND, "checkout", head) or return false
         system(COMMAND, "rebase") or return false
       end