full paths for .gitignore + ignore .DS_Store files

Without this then we can not add files to "sbin" directory
under nanobsd/Files/usr/local/sbin.

Add .DS_Store for mac people.
Merge branch 'git_ignore' of https://github.com/alfredperlstein/freenas into alfredperlstein-git_ignore
Merge branch 'alfredperlstein-git_ignore'