Merge branch 'ab/test-lib'

Test framework clean-up.

* ab/test-lib:
  test-lib-functions: assert correct parameter count
  test-lib-functions: remove bug-inducing "diagnostics" helper param
  test libs: rename "diff-lib" to "lib-diff"
  t/.gitattributes: sort lines
  test-lib-functions: move function to lib-bitmap.sh
  test libs: rename gitweb-lib.sh to lib-gitweb.sh
  test libs: rename bundle helper to "lib-bundle.sh"
  test-lib-functions: remove generate_zero_bytes() wrapper
  test-lib-functions: move test_set_index_version() to its user
  test lib: change "error" to "BUG" as appropriate
  test-lib: remove check_var_migration

diff --cc t/README
Simple merge

diff --cc t/t5318-commit-graph.sh
Simple merge

diff --cc t/t6500-gc.sh
Simple merge

diff --cc t/t9300-fast-import.sh
Simple merge

diff --cc t/test-lib-functions.sh
Simple merge

diff --cc t/test-lib.sh
Simple merge