#187 AutoSave interval not read on startup

[Giermann]

I noticed that the AutoSave interval is not being stored or kept among sessions.
After researching this problem I found, that it's stored correctly in the Registry, but is never being read again - instead it always defaults to 10 minutes.

The attached patch fixes this by reading the registry on the first call of CAutoSave::GetDelay().
Further I fixed the resulting issue that enabling the interval when it's disabled does not re-init to 10 minutes and I modified the explaination text to match the extension ".autosave" instead of ".backup".

[Giermann]

push
Do I need to set some review flags or something?

[Don Lucas]

The attached patch has been successfully applied to version 2.90.00. This version will be released soon. Many thanks to user Giermann, and sorry for the delay.