eliminated unnecessary cd and failing substitution

Changing the working directory in a sub-subshell
does not change the working directory of the executing
shell.

The substitution was broken for me on _all_ my machines,
so I started looking into the business.
Adding a fix for the DISABLE_UNTRACKED_FILES_DIRTY option.
Merge pull request #1775 from marcusmueller/fixupgradetool

fix for failing substition & eliminated unnecessary cd
Merge pull request #1834 from croach/disable_untracked_files_dirty_fix

Adding a fix for the DISABLE_UNTRACKED_FILES_DIRTY option.
fix the open command in linux using xdg-open
Merge pull request #1849 from lemieux/master

Fix for Jira plugin on Linux
Merge branch 'master' of git://github.com/robbyrussell/oh-my-zsh