open_terminal_here.py changes directory, preventing unmount

[Mark Wilkinson]

With the Mounter docklet and Open Terminal Here helper running, the helper process can prevent the user from unmounting a removable device because it changes directory and then stays there.

Steps to reproduce:
1. Insert a removable storage device like a USB stick.
2. Right click the device in Docky and choose Open Terminal Here.
3. Close the terminal that just opened.
4. Attempt to unmount the USB stick. The device won't unmount because the helper process has the USB stick as its current directory.

[Robert Dyer (psybers)]

Fixed in rev 37.