consistent return of pc_schema_from_xml : NULL on failure
cu_pc_sort.c currently uses a mix of spaces and tabs. This commit changes all the tabs to spaces.
* PC_Sort and PC_IsSorted * fixing -Wdeclaration-after-statement warnings * using sort_r for a portable definition of qsort_r/qsort_s * uncompression fallback for lazperf/is_sorted * NEWS updated, sort_r github reference and README added