Use git to put a version in configure

CI has been using this for a long time.  Now that generated files are
no longer in the repository, new clones require autotools already and
adding a git requirement doesn't seem like a big burden.

.gitlab-ci.yml

@@ -18,7 +18,6 @@ prepare:
   stage: prepare
   script:
   - find -path ./.git -prune -o -type f | xargs tools/style-check.sh
-  - sed -i '/^AC_INIT/s/,.*/,m4_esyscmd_s([git describe --dirty]),/' configure.ac
   - ./autogen.sh
   - ./configure
   - make dist

README

@@ -71,6 +71,8 @@ the project's website at http://www.sane-project.org/.
 
         - gettext (>=0.19.8)
 
+        - git (>= 2.1.4)
+
 SANE should build on most Unix-like systems. Support for OS/2, MacOS X, BeOS,
 and Microsoft Windows is also available. For more details look at the
 operating system specific README.* files. For a detailed support matrix, see:

configure.ac

@@ -5,7 +5,7 @@ dnl  Set up autoconf and automake
 dnl  When preparing a release, modify the numeric version components
 dnl  and remove the git suffix.
 dnl ******************************************************************
-AC_INIT([sane-backends],[1.0.27git],
+AC_INIT([sane-backends],m4_esyscmd_s([git describe --dirty]),
         [sane-devel@alioth-lists.debian.net])
 AC_PREREQ([2.69])               dnl minimum autoconf version required
 AC_CONFIG_MACRO_DIR([m4])