RF: refactor dropbox stuff; BF fix win drive-letter
NF: try to detect if a file is under version control; needs work

- if VC'd, warn as appropriate; not as serious as in dropbox
- needs more work, e.g., file vs dir in get_git
- get errors in log, probably from stderr from _sys_call
    ERROR fatal: Not a git repository
- uncomment is_version_controlled in destroy()