Btrfs-progs: tool to visualize fragmentation

Btrfs-progs: tool to visualize fragmentation

This tool draws per-chunk pngs representing the allocation map. A black
or colored dot means the block is allocated.
The output is written to a subdirectory, together with an index.html to be
viewed in a browser.
There are options to control whether color should be used and which block
group types should be printed.
To build, you need to have libpng and libgd installed. It is not part of
the 'all' target, so please build it explicitely with make btrfs-fragments.

A (rather untypical) example can be seen at

http://sensille.com/fragments

Please regard this as a first scratch version and feel free to improve it :)

Signed-off-by: Arne Jansen <sensille@gmx.net>