Problem: Invalid memory access in read_redo(). (gy741)
Solution: Convert the replacement character back from a negative number to
CR or NL. (hint by Dominique Pelle, closes#2616)
Problem: Using ":undo 0" leaves undo in wrong state.
Solution: Instead of searching for state 1 and go above, just use the start.
(Ozaki Kiichi, closes#2595)
Problem: seq_cur of undotree() wrong after undo.
Solution: Get the actual sequence number instead of decrementing the current
one. (Ozaki Kiichi, closes#2319)
Problem: ":earlier" and ":later" do not work after startup or reading the
undo file.
Solution: Use absolute time stamps instead of relative to the Vim start
time. (Christian Brabandt, Pavel Juhas, closes#1300, closes
#1254)
