Add code to retrieve or construct a revlog delta

Add fileopener to move some pathname knowledge from filelog to repository

Make revision code slightly faster

Only use lazy indexing for big indices and avoid the overhead of the lazy index in the small index case.

Make lazyindex load slightly faster

Simplify checkout slightly, replace checkdir with os.makedirs

Sort files on check-in for good I/O patterns

Make compression more intelligent: - we don't attempt to compress things under 44 bytes (empirical) - we check whether larger objects actually compress - we tag objects to indicate their compression NUL means uncompressed and starts with NUL x means gzipped and starts with x (handy) u means uncompressed, drop the u

Add script for doing conversion of repo from oldstyle to newstyle

Move hg from storing files in data with base64 encoding to full pathnames with .i and .d extensions. This means we naturally get good FS layout, and cp and tar fix things up nicely rather than pessimizing layout.