bug, refactor, test: make pragma history_length work interactively history_length could be set interactively, but it was never used to set readline/pyreadline3's internal state. Using the pragma setting on the roundup-admin command line did set readline's state. Also refactored 2 calls to self.readline.get_current_history_length() into one call and storing in a variable. Also changed method for creating history strings for printing. Tests added for history_length pragma on cli and interactive use. Added test for exiting roundup-admin with EOF on input. Added test for 'readline nosuchdirective' error case. Added test to readline with a command directive to set an internal variable. This last one has no real test to see if it was successful because I can't emulate a real keyboard/tty which is needed to test.

<!--
 This is the default body that is displayed when people visit the
 tracker. The tag below lists the currently open issues. You may
 replace it with a greeting message, or a different list of issues or
 whatever. It's a good idea to have the issues on the front page though
-->
<span tal:replace="structure python:db.issue.renderWith('index',
    sort=[('-', 'activity')], filter=['status'],
    columns=['activity','title','creator'],
    filterspec={'status':['1','2','4']})" />