REPL history: instructive warning for old-style history files.

base/REPL.jl

@@ -264,13 +264,17 @@ REPLHistoryProvider(mode_mapping) =
  REPLHistoryProvider(String[], nothing, 0, -1, IOBuffer(),
  nothing, mode_mapping, Uint8[])
 
+const invalid_history_message = """
+Invalid history format. If you have a ~/.julia_history file left over from an older version of Julia, try renaming or deleting it.
+"""
+
 function hist_from_file(hp, file)
  hp.history_file = file
  seek(file, 0)
  while !eof(file)
  mode = :julia
  line = utf8(readline(file))
- line[1] == '#' || error("invalid history entry")
+ line[1] == '#' || error(invalid_history_message)
  while true
  m = match(r"^#\s*(\w+)\s*:\s*(.*?)\s*$", line)
  m == nothing && break
@@ -279,7 +283,7 @@ function hist_from_file(hp, file)
  end
  line = utf8(readline(file))
  end
- line[1] == '\t' || error("invalid history entry")
+ line[1] == '\t' || error(invalid_history_message)
  lines = UTF8String[]
  while true
  push!(lines, chomp(line[2:end]))