Merge branch 'pw/xdiff-classify-record-in-histogram'

"diff --histogram" optimization. * pw/xdiff-classify-record-in-histogram: xdiff: drop unused flags parameter from recs_match xdiff: drop xpparam_t parameter from histogram cmp_recs() xdiff: drop CMP_ENV macro from xhistogram xdiff: simplify comparison xdiff: avoid unnecessary memory allocations diff histogram: intern strings