Development mode has been determined by whether the launcher is in git
repo
or not. This could be wrong when the launcher is installed to
subdirectory of other project's git repo, such as jhbuild. It is normal
to install compiled output to subdirectory of your jhbuild.
Changed logic gets the first commit hash of current git repo and
compares it with gst-devtools' the first commit hash.
https://bugzilla.gnome.org/show_bug.cgi?id=744781