Small test-helper programs have been consolidated into a single
binary.

* nd/combined-test-helper: (36 commits)
  t/helper: merge test-write-cache into test-tool
  t/helper: merge test-wildmatch into test-tool
  t/helper: merge test-urlmatch-normalization into test-tool
  t/helper: merge test-subprocess into test-tool
  t/helper: merge test-submodule-config into test-tool
  t/helper: merge test-string-list into test-tool
  t/helper: merge test-strcmp-offset into test-tool
  t/helper: merge test-sigchain into test-tool
  t/helper: merge test-sha1-array into test-tool
  t/helper: merge test-scrap-cache-tree into test-tool
  t/helper: merge test-run-command into test-tool
  t/helper: merge test-revision-walking into test-tool
  t/helper: merge test-regex into test-tool
  t/helper: merge test-ref-store into test-tool
  t/helper: merge test-read-cache into test-tool
  t/helper: merge test-prio-queue into test-tool
  t/helper: merge test-path-utils into test-tool
  t/helper: merge test-online-cpus into test-tool
  t/helper: merge test-mktemp into test-tool
  t/helper: merge (unused) test-mergesort into test-tool
  ...