Merge branch 'sg/bash-prompt'

* sg/bash-prompt: bash prompt: mention that PROMPT_COMMAND mode is faster bash prompt: avoid command substitution when finalizing gitstring bash prompt: avoid command substitution when checking for untracked files bash prompt: use bash builtins to check stash state bash prompt: use bash builtins to check for unborn branch for dirty state bash prompt: combine 'git rev-parse' for detached head bash prompt: combine 'git rev-parse' executions in the main code path bash prompt: use bash builtins to find out current branch bash prompt: use bash builtins to find out rebase state bash prompt: run 'git rev-parse --git-dir' directly instead of __gitdir() bash prompt: return early from __git_ps1() when not in a git repository bash prompt: print unique detached HEAD abbreviated object name bash prompt: add a test for symbolic link symbolic refs completion, bash prompt: move __gitdir() tests to completion test suite bash prompt: use 'write_script' helper in interactive rebase test bash prompt: fix redirection coding style in tests