store a configuration hash in cache files

[Peter Johansson]

Some of the configuration options affects the statistics stored in cache files. I think we should store those setting in the cache file. For example the codons that determines what is code and what is a comment should be store, but also other possible settings such as stop-on-copy when we allow that to be configured.

The idea is that this information then should be compared with the configuration at runtime. If they are not equal we should... yes that is an open question, but svndigest should react somehow. Either we could halt (unless some option flag was given) or we can ignore the cache file with a small notice to the user.

If we find no hash at all, I think, should be treated as the hash equals the current configuration. Also when we add new configuration option in Configuration class the hash should not change as long as we use the same setting as before.

[Peter Johansson]

I think this is important and should be included in 0.8

[Peter Johansson]

fixed in r1122 and 1124