Bump libzip requirement to >= 0.10.

Bump libzip requirement to >= 0.10.

We now use zip_int64_t and zip_get_num_entries() for example, which
requires at least libzip 0.10. This version was released in 03/2012,
which is old enough that we don't necessarily have to do a work-around
for older versions. Thus, simply bump the requirement to >= 0.10.