Compressed pristines and in-database pristine storage
-----------------------------------------------------

NOTE: This branch depends on ^/subversion/branches/multi-wc-format.

WC format 32 will get support for storing (small) pristine files
directly in the WC-DB as blobs in the PRISTINES table, and also for
compressing pristines with LZ4.

The current WC format 31 will remain fully supported.

The 'svn cleanup' command will grow a new option:

    svn cleanup --compress-pristines

that will, if compressed pristines are supported by the working copy
format, compress any uncompressed pristine files, possibly removing
them and storing their contents in the working copy database.

Upgdading to format 32 will _not_ automatically compress pristines.