added change user phase into ucrawl-tweet command "conf". fixed some bugs

 - fixed bugs in ucrawl-tweet:
    - died when $@->twitter_error is not defined
    - tables are dropped and created when
      you give empty answer to the question 'force create?'
      default should have been 'no'.
    - command "status" is finished unexpectedly when empty line comes from STDIN

 - added tests for ucrawl-tweet:
    - fail tests for command "conf"
    - command "status" with STDIN