SI-4714 Initialize history while initializing the REPL's reader

It was possible to get a command into the REPL before the history
recording object was set and so the command would be lost in the sands
of time. This fix just moves the initialization of the history object
into the JLineReader constructor, out of the post-init hook.

@paulp how is this going to break things? Also, I don't have a clue how to automate the testing of this.