Automatically exclude alt links and template files

unless yadm.auto-exclude is set to false (#234, #465).

Alt files exclude pattern will be written to $GIT_DIR/info/exclude.yadm-alt and
encrypt files exclude patthern to ...yadm-encrypt. Then these two files will be
merged together and added to $GIT_DIR/info/exclude whenever one of them has
changed.

test/test_alt.py

@@ -217,6 +217,29 @@ def test_auto_alt(runner, yadm_cmd, paths, autoalt):
                 assert str(paths.work.join(source_file)) not in linked
 
 
+@pytest.mark.usefixtures("ds1_copy")
+@pytest.mark.parametrize("autoexclude", [None, "true", "false"])
+def test_alt_exclude(runner, yadm_cmd, paths, autoexclude):
+    """Test alt exclude"""
+
+    # set the value of auto-exclude
+    if autoexclude:
+        os.system(" ".join(yadm_cmd("config", "yadm.auto-exclude", autoexclude)))
+
+    utils.create_alt_files(paths, "##default")
+    run = runner(yadm_cmd("alt", "-d"))
+    assert run.success
+
+    run = runner(yadm_cmd("status", "-z", "-uall", "--ignored"))
+    assert run.success
+    assert run.err == ""
+    status = run.out.split("\0")
+
+    for link_path in TEST_PATHS:
+        flags = "??" if autoexclude == "false" else "!!"
+        assert f"{flags} {link_path}" in status
+
+
 @pytest.mark.usefixtures("ds1_copy")
 def test_stale_link_removal(runner, yadm_cmd, paths):
     """Stale links to alternative files are removed

test/test_unit_exclude_encrypted.py

@@ -9,7 +9,12 @@ import pytest
 def test_exclude_encrypted(runner, tmpdir, yadm, encrypt_exists, auto_exclude, exclude):
     """Test exclude_encrypted()"""
 
-    header = "# yadm-auto-excludes\n# This section is managed by yadm.\n# Any edits below will be lost.\n"
+    header = """\
+# yadm-auto-excludes
+# This section is managed by yadm.
+# Any edits below will be lost.
+# yadm encrypt
+"""
 
     config_function = 'function config() { echo "false";}'
     if auto_exclude: