Further code cleanup for the backup suite

Further code cleanup for the backup suite

Protect butm.h against multiple inclusion
Prototype more functions for internal use in bucoord
Remove some unused variables
Include additional headers as required
Prototype exported functions in budb
Make SendReturnList helper function generic, by using a void * rock

Reviewed-on: http://gerrit.openafs.org/http://gerrit.openafs.org/168
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>