fixed update not working with undo/redo

#202
Merge branch 'staging' of https://github.com/cs2103aug2014-w13-1c/main into jolly/gui
added error messages for undo/redo buttons
first character of command can no longer be a space

#198
more fixes for eliminating spaces as the first character in a command

now works with strings with lots of spaces at the front!
Merge branch 'dat/model' into staging