sparse-xpow.cc: Improve consistency between sparse and full matrices (bug #63080) sparse-xpow.cc: Return 0x0 matrix for empty inputs of all sizes. Return early for all-zeros matrix with positive power. Add FIXME for all-zeros matrix with negative power. Add BISTs.

publish_TEST_FILES = \
  %reldir%/publish.tst \
  %reldir%/test_script.m \
  %reldir%/test_script_code_only.m \
  %reldir%/test_script_empty.m \
  %reldir%/test_script_example.m \
  %reldir%/test_script_head_only.m

TEST_FILES += $(publish_TEST_FILES)