Merge branch 'ab/tests-various-fixup'

Merge branch 'ab/tests-various-fixup'

Various test updates.

* ab/tests-various-fixup:
  rm tests: actually test for SIGPIPE in SIGPIPE test
  archive tests: use a cheaper "zipinfo -h" invocation to get header
  upload-pack tests: avoid a non-zero "grep" exit status
  git-svn tests: rewrite brittle tests to use "--[no-]merges".
  git svn mergeinfo tests: refactor "test -z" to use test_must_be_empty
  git svn mergeinfo tests: modernize redirection & quoting style
  cache-tree tests: explicitly test HEAD and index differences
  cache-tree tests: use a sub-shell with less indirection
  cache-tree tests: remove unused $2 parameter
  cache-tree tests: refactor for modern test style