how can I know the blender version which have been used to save a blend file?

I need to write an update script, and thus I need to know if the current blend file has been written by an older version of blender.
I’m sure this propertie exists, because blender warn you when you open a file with an old version.
I’ve found this too :

It could be old, but anyway, I don’t know how to read in “little indian”.

Any help?