Expose _SC_MIN_HOLE_SIZE as MIN_HOLE_SIZE via getconf(1).

[jmmv]

Summary

The _SC_MIN_HOLE_SIZE pathconf(2) property provides information on
whether a file system supports holes (sparse files) or not. I intend to use
this information in the ls(1) shell tests, which attempt to create very
large sparse files and spuriously fail if their work directory happens to be
on, e.g., tmpfs.

[ngie]

I just did the same thing in r304694 :/...