Define the types which will be used to communicate between the
different parts of the inspection code. The main types are:
fs corresponds to ‘struct inspect_fs’ in C code
root no direct correspondence with the C code, but in the C
code, ‘inspect_fs’ was overloaded to store roots
inspection_data
the inspection data which is incrementally collected about
each filesystem as we perform inspection steps
Other types have simple and obvious correspondences with the
equivalent C code.
Add some utility function which will be used by inspection.
Note that this commit has no effect on its own, it just links extra
dead code into the daemon.
