illumos gate

RFE: We need utilities to create and list holes (sparse files). Main purpose for now is for the nfs testsuite but AFAIK the utilities have generic use cases, too.

Proposed functionality would be:
- lsholes - prints all data and holes section.
The lsholes utility should print by default all data and hole section with absolute offset and size. There should be options to specify alternative output formats, start+end offsets and an option just to test whether a file as any holes at all.

- mkholes - creates or modifies a file to have holes
basically working like mkfile but takes a list of holes as input via command line options or via a file (this is needed since the size of arguments is limited by |ARG_MAX|&co. and we need to create sparse files which have a lot more holes in there).