Merge branch 'ee/clean-remove-dirs'

Replace "is this subdirectory a separate repository that should not be touched?" check "git clean" does by checking if it has .git/HEAD using the submodule-related code with a more optimized check. * ee/clean-remove-dirs: read_gitfile_gently: fix use-after-free clean: improve performance when removing lots of directories p7300: add performance tests for clean t7300: add tests to document behavior of clean and nested git setup: sanity check file size in read_gitfile_gently setup: add gentle version of read_gitfile