bug#60143: 29.0.60; command `undo-redo` don't restore cursor position

[yinz Liu]

aaaa ! bbbb @ cccc #

1. when cursor at position "#", call `undo', cursor jump to "@"

2. when cursor at position "@", call `undo-redo', text "cccc" restore,

   but cursor still remain in "@", don't move to "#".

my workaround fow now:

in function primitive-undo :

change L3624 to : `(goto-char (+ pos (length string)))`