Added missing attr initialization (ConsoleWidget.history_index).
Without this initialization if the user press UP/Down keys and there the
ConsoleWidget._history still empty the ConsoleWidget fail until the user enter some command.
Merge branch 'console_history_index'
Merge branch 'master' of git://github.com/ninja-ide/ninja-ide
Merge pull request #1284 from malderete/master

Missing attribute in the __init__