export cache

[Peter Johansson]

According to the manual svndigest-copy-cache will only copy cache to a target if the target has the same files structure as the root tree. This is fine as default but perhaps we should allow the user to soften this restriction. I'm thinking something similar to the --parents switch in mkdir, in other words,

svndigest-copy-cache -p -r here -t there should create the necessary directories in there.