Merge branch 'dl/stash-cleanup'

Documentation, code and test clean-up around "git stash". * dl/stash-cleanup: stash: declare ref_stash as an array t3905: use test_cmp() to check file contents t3905: replace test -s with test_file_not_empty t3905: remove nested git in command substitution t3905: move all commands into test cases t3905: remove spaces after redirect operators git-stash.txt: be explicit about subcommand options