Patch to add md5/sha hash tokens for use by File Entity Paths (fe_paths) for pairtree content addressable storage (CAS)

Hi,

I have created a little patch that adds tokens for filehash so they may be used in other modules like file entity path (fe_paths) and possibly filefield_paths (fe_paths replaces this though).

This is useful to be able to change the way drupal stores files in paths according to the Content Addressable Storage (CAS http://en.wikipedia.org/wiki/Content-addressable_storage) pairtree spec by CDLib: http://www.slideshare.net/jakkbl/dcc-pair-posterppt

As well as the tokens for full md5, sha-1, sha-256, I have added two levels of pair tokens for each. So for example a md5 of 3998b02c5cd2723153c39701683a503b the file-md5-1 will be 39 and the file-md5-2 will be 98.

This means that in fe_paths you can set a token like:

/[file:file-md5-1]/[file:file-md5-2]/

And see storage paths like /files/39/98/

I have run this patch against Coder code review and it passed checks except for this existing one on filehash.install (I haven't touched this file, so it's unrelated):

filehash.install - severity: normalLine -1: @file block missing (Drupal Docs)

I also added a check on filehash_file_load to make sure the file variable was an object as sometimes a string is passed instead and it causes an error passing to filehash_save.

Please review and if you like it put it in -dev?

Thanks,
Christiaan Kortekaas