Updated Serbian translation
render:  Show rendering errors in a dialog

Abort rendering when an error is encountered in the pipeline,
show the error so that the user actually knows something went wrong.

Fixes bug #635874
ui/filelisterrordialog: Set the GTK box orientation to be vertical

This also updates the GtkBuilder file's syntax to Glade's latest tastes
render: Show a more human-readable message when an error occurs in the pipeline

Hide the gory details in a GTK Expander widget
Updated Polish translation
Make the dogtail tests work again with the Clutter timeline, cleanup code
mainwindow: Ensure "Clip properties" is the focused context tab on startup
previewers: Use proper debug statements instead of prints for the thumbnailer

Also rename some internal variables
previewers: General code cleanup
Updated Spanish translation
bin: Make it possible to source pitivi-git-environment
script: Add option to force autogen of modules
timeline: Removing an effect should not trigger graphical updates.
bin: Make it possible to run a command right after running pitivi-git
bin: disable docbook if disabling docs in pitivi-git
bin: Do not change directory if sourced or launching a command

+Rework the way we set PS1
Clarify a bit the comments
Remove unused variable
Set MODULES_CORE in a single place
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