redmine-backporter.rb: improve mygets

* tool/redmine-backporter.rb (mygets): newline to finish, fix DEL
  code, erase the last character at DEL/BS, and use \C escapes.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49343 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/redmine-backporter.rb

@@ -202,17 +202,16 @@ def mygets
   line = ''
   while 1
     case c = console.getch
-    when "\r"
+    when "\r", "\n"
       puts
       line << c
       return line
-    when "\x07", "\b" # DEL/BS
-      print "\b"
-      line.chop!
-    when "\x15" # C-u
+    when "\C-?", "\b" # DEL/BS
+      print "\b \b" if line.chop!
+    when "\C-u"
       print cls
       line.clear
-    when "\x04" # C-d
+    when "\C-d"
       return nil if line.empty?
       line << c
     else