Calculate the size of the backing store file.
Calculate the size of the backing store file.

A size can be specified in absolute terms (suffix: k, m, g, t supported),
but also as a percentage of the filesystems free space (suffix '%').

If the specified size is larger than an off_t can cope, we bisect 
repeatedly until it can.

If the size exceeds the available space of the filesystem, we truncate
to 80% of the free space.

Then round down to an integral number of blocks, sized by the larger
of the filesystem blocksize and the pagesize.

This was tricker than I'd expected...



git-svn-id: 7d4b18ab7d176792635d6a7a77dd8cbbea8e8daa@175 d4fa192b-c00b-0410-8231-f00ffab90ce4

wikimedia/operations-debs-varnish,ssm/pkg-varnish,CartoDB/Varnish-Cache,ssm/pkg-varnish,CartoDB/Varnish-Cache,wikimedia/operations-debs-varnish,wikimedia/operations-debs-varnish,ssm/pkg-varnish,wikimedia/operations-debs-varnish,ssm/pkg-varnish,wikimedia/operations-debs-varnish,CartoDB/Varnish-Cache,ssm/pkg-varnish