[Libguestfs] [PATCH v2] Add tune2fs command.

[Richard W.M. Jones]

The changes since the previous patch:

 - safe ADD_ARG macro for adding arguments to a fixed size stack array

 - support for testing functions that return RHashtable, ie. tune2fs-l.

 - add tests that set (tune2fs) and get (tune2fs-l) various parameters.

 - only one 'intervalbetweenchecks' parameter (in seconds)

Rich.