Log exception before converting it to a string

Also, improved error when a feed has the wrong root element.
Updated Swedish translation
GtkStatusIcon.set_blinking has been removed from GTK 3
Fix typo ("contraint")
Add spacer lines for readability in "0install show" output
Fixed exception reporting on Python 3
Added support for Tulip mainloop

Tulip is a pure-Python mainloop for Python >= 3.3. With Tulip, there is no
need for python-gobject.

Tulip is currently experimental, but as it is only used when gobject is not
present, supporting it shouldn't do any harm.
"0install add" now prints a warning if the target has a replaced-by field
Don't abort running an app if updating fails due to a read-only filesystem
Cope with read-only cache in Fetcher.download_and_import_feed

Report read-only cache errors like other download errors so that Driver doesn't
abort.
Recognise .deb files with data.tar.xz
Use copy instead of symlink for latest app selections document on Windows
Use new version of 0install-runenv-cli helper
Support old and new versions of runenv-cli on Windows
Search system paths for native binaries

Previously, each <package-implementation> had to give the absolute path of
the main binary. This causes unnecessary duplication e.g.

  <package-implementation package="graphviz" distributions="RPM Debian Arch" main="/usr/bin/dot"/>
  <package-implementation package="graphviz" distributions="MacPorts" main="/opt/local/bin/dot"/>
  <package-implementation package="graphviz" distributions="Ports" main="/usr/local/bin/dot"/>

Now, if the main value isn't found, we search the other system paths for the
binary. We also now allow non-absolute values (e.g. main='dot'). However, that
will break older versions of 0install and so should be avoided for now.
Add an --xml output option to the testrunner
Make the coverage output as --xml as well
Add the .xml test reports to the ignored files
Added "0install search"

This sends the query to the mirror server and displays the results.
Added <remove> recipe step, and added optional `dest` attribute to <archive>

 - remove takes a single "path" attribute, and works on files and folders
 - `dest` unpacks the archive to a subfolder
 - `dest` locations for both <archive> and <rename> steps are created as needed