Revert 2013-01-31 change that decides coding system before backing up

It causes a more serious problem than the one it solves.
This closes bug#18141, and reopens bug#13522.

* lisp/files.el (basic-save-buffer-2): Revert 2013-01-31 change.

* src/fileio.c: Revert 2013-01-31 change.
(choose_write_coding_system): No longer callable from Lisp.
Move last piece back here from Fwrite_region.
(Fwrite_region, syms_of_fileio): Update for above changes.

* test/automated/data/files-bug18141.el.gz: New file.
* test/automated/files.el (files-test-bug-18141-file):
New variable and test.

3 files changed, 24 insertions, 0 deletions

diff --git a/test/ChangeLog b/test/ChangeLog
index d68c5b6bb07..d5c5e58f09c 100644
--- a/test/ChangeLog
+++ b/test/ChangeLog
@@ -1,3 +1,9 @@
+2014-08-11  Glenn Morris  <rgm@gnu.org>
+
+        * automated/data/files-bug18141.el.gz: New file.
+        * automated/files.el (files-test-bug-18141-file):
+        New variable and test.  (Bug#18141)
+
 2014-08-07  Glenn Morris  <rgm@gnu.org>
 
         * automated/Makefile.in (check-tar): Remove, no longer needed.
diff --git a/test/automated/data/files-bug18141.el.gz b/test/automated/data/files-bug18141.el.gz
new file mode 100644
index 00000000000..53d463e85b5
--- /dev/null
+++ b/test/automated/data/files-bug18141.el.gz
diff --git a/test/automated/files.el b/test/automated/files.el
index 44816bc33f5..8db06f7dfe3 100644
--- a/test/automated/files.el
+++ b/test/automated/files.el
@@ -148,6 +148,24 @@ form.")
               (should (file-test--do-local-variables-test str subtest))))))
     (ad-disable-advice 'hack-local-variables-confirm 'around 'files-test)))
 
+(defvar files-test-bug-18141-file
+  (expand-file-name "data/files-bug18141.el.gz" (getenv "EMACS_TEST_DIRECTORY"))
+  "Test file for bug#18141.")
+
+(ert-deftest files-test-bug-18141 ()
+  "Test for http://debbugs.gnu.org/18141 ."
+  (skip-unless (executable-find "gzip"))
+  (let ((tempfile (make-temp-file "files-test-bug-18141" nil ".gz")))
+    (unwind-protect
+        (progn
+          (copy-file files-test-bug-18141-file tempfile t)
+          (with-current-buffer (find-file-noselect tempfile)
+            (set-buffer-modified-p t)
+            (save-buffer)
+            (should (eq buffer-file-coding-system 'iso-2022-7bit-unix))))
+      (delete-file tempfile))))
+
+
 ;; Stop the above "Local Var..." confusing Emacs.