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