fallocate: Add "--dig-holes" options and minor fixes

[Rodrigo Campos <rodrigo@sdfg.com.ar>]

Hi,

As discussed in this[1] gmane thread, I'm submitting the funtionality to dig
holes as part of the fallocate(1) command.

When using this option, the file is searched for chunks of '\0's and digs a hole
when possible. The end result should (if a hole was found) an sparse file
created in-place.

The patchset consist of 3 patches, the first one:

	[PATCH 1/3] fallocate: Clarify that space can also be deallocated

is just a fix to make clear that the fallocate tool as already is, is capable of
dellocations too (not only preallocations).

The next 2 patches are:

	[PATCH 2/3] fallocate: Hide #ifdef tricks to call fallocate in a

	Which creates a function that has the #ifdef, that will be useful when
we call fallocate from different places in the code (i.e. in the next patch)

	[PATCH 3/3] fallocate: Add "--dig-holes" option

	That just adds the option and updates the manpage.


Comments and suggestions totally welcome! :)




Thanks a lot,
Rodrigo

[1]: http://article.gmane.org/gmane.linux.utilities.util-linux-ng/8415