Resolve "xscanimage crashes with test backend"

Closes #25

See merge request !4

Failure to call sane_exit() which causes issues in genesys backend
termination.

Resolve "scanadf -L crashes"

Closes #22

See merge request !2

scanadf.c: implement dedicated exit function to prevent SIGSEGV

Closes #19

See merge request !1

Also fixes up minor typos in include/sane/sanei.h.

This reverts commit 41c62621 to get
the pipeline green again.  It looks like the broken pipeline caused
the website pipeline to fail on downloading the frontends artifact.
Not sure why it hasn't failed earlier.

There is no point in requesting a --dirty'd description when all you
have is a clean checkout.

The .gitlab-ci.yml files are *not* Makefiles ;-)

The old version is licensed under the Artistic License 1.0 which isn't
compatible with the GPL and arguably non-free.
Signed-off-by: Nils Philippsen <nils@redhat.com>
 * fix trailing whitespace

- when SANE_CAP_ALWAYS_SETTABLE doesn't exit, let gsg_set_sensitivity()
  call gtk_widget_set_sensitive()

	  popup, based on a patch by
	  Jonas Berlin <xkr47@outerspace.dyndns.org>

	- handling of SANE_STATUS_WARMING_UP after sane_start() calls
	- xscanimage's progress dialog improvement

at sane_start time, e.g. no documents. Formerly the button was left
inactive.
This bug already got on my nerves for quite some time now 8-).