apply my change from my_v2_1 branch : 8ebd25d
  - allow user to select a scene by single clicking it. (previously, it required a double click, which gets very irritating very quickly..)
misc labelling change.
auto-save all documents when project is closed or cocosbuilder is about to
 be exited. also when a save is requested, save all dirty documents..

Conflicts:
	CocosBuilder/ccBuilder/CocosBuilderAppDelegate.m
log the ccbi file version (for debugging purposes).
apply change 43975f3 from my_v2_1 branch : it turns out CocosBuilder does not always detect document changes properly. e.g. if you set the CCControl selector property, it doesn't notice that it's been set. workaround is to save all currently open ccb documents regardless of whether they have the dirtyFlag set or not.
apply my change from my_v2_1 branch: 39c7cd0
- CocosBuilder was not serializing default opacity of 255. As it turns out CCLayerColor sets
a default opacity of 0. corrected this so that both assume a default opacity of 0..