Document that cache.linesize is 0 if unknown
Document that cache.linesize is 0 if unknown

This happens at least on some Power machines (sysfs gives 0 for most fields on some cache levels).

Thanks to Erik Schnetter for the report.

This commit was SVN r5406.

shekkbuilder/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc,ggouaillardet/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc,shekkbuilder/hwloc