[Scons-dev] more on cache

[Tom Tanner (BLOOMBERG/ LONDON)]

for reasons I've yet been able to determine, it seems possible for the 'csig' value in the get_ninfo() in the FS class to get set to 'None'. This causes all sorts of fun with the cache. This can be fixed by deleting the .scons-dblite file, but it's not terribly apparent at the moment how it gets into this state and if it's possible to recover better.