autogen.sh: Error out when gnulib-tool exit with non-zero

As the local patches to Gnulib tool often fail to apply after updating
the submodule, it would be good to stop processing there.
msgfilter: Add 'quot' and 'boldquot' built-in filters
examples: Add new example 'hello-c-gnome3'
examples: Fix dependencies of hello-c-gnome3
NEWS: Mention msgfilter quot and msgfilter boldquot
msgfmt: Allow any whitespace as a list separator in LINGUAS
examples: Utilize msgfmt --desktop
examples: Utilize GSettings in hello-c-gnome3 example
examples: Add missing XML files to hello-c-gnome3 example
msgfmt: Simplify LINGUAS parsing
msgfmt: Fix commit cfac1548
examples: Don't error out from configure in hello-c-gnome3

The configure script shouldn't fail even if there is a fatal
error, to allow the toplevel autogen.sh to regenerate POT files.
* hello-c-gnome3/configure.ac: Don't error out, but warn user.
xgettext: Strip multiple ".in" suffixes from the file name.

* xgettext.c (main): Strip multiple ".in" suffixes.
autogen.sh: Use included gettext-tools for bootstrap

To regenerate POT files, autogen.sh had an implicit dependency on
gettext-tools installed on system.  This prohibited to use any new
features in our examples.  Let autogen.sh use included version of
gettext-tools, by prepending $builddir to the PATH.