Merge branch 'da/xdiff-w-sign-compare-workaround'

Noises from "-Wsign-compare" in the borrowed xdiff code has been
squelched.

* da/xdiff-w-sign-compare-workaround:
  xdiff: avoid signed vs. unsigned comparisons in xutils.c
  xdiff: avoid signed vs. unsigned comparisons in xpatience.c
  xdiff: avoid signed vs. unsigned comparisons in xhistogram.c
  xdiff: avoid signed vs. unsigned comparisons in xemit.c
  xdiff: avoid signed vs. unsigned comparisons in xdiffi.c
  xdiff: move sign comparison warning guard into each file