patch 9.0.1234: the code style has to be checked manually

Problem:    The code style has to be checked manually.
Solution:   Add basic code style checks in a test.  Fix or avoid uncovered
            problems.

src/testdir/test_codestyle.vim

@@ -0,0 +1,45 @@
+" Test for checking the source code style.
+
+def Test_source_files()
+  for fname in glob('../*.[ch]', 0, 1)
+    exe 'edit ' .. fname
+
+    cursor(1, 1)
+    var lnum = search(' \t')
+    assert_equal(0, lnum, fname .. ': space before tab')
+
+    cursor(1, 1)
+    lnum = search('\s$')
+    assert_equal(0, lnum, fname .. ': trailing white space')
+
+    # some files don't stick to the Vim style rules
+    if fname =~ 'iscygpty.c'
+      continue
+    endif
+
+    # Examples in comments use "condition) {", skip them.
+    # Skip if a double quote or digit comes after the "{".
+    # Skip specific string used in os_unix.c.
+    # Also skip fold markers.
+    var skip = 'getline(".") =~ "condition) {" || getline(".") =~ "vimglob_func" || getline(".") =~ "{\"" || getline(".") =~ "{\\d" || getline(".") =~ "{{{"'
+    cursor(1, 1)
+    lnum = search(')\s*{', '', 0, 0, skip)
+    assert_equal(0, lnum, fname .. ': curly after closing paren')
+
+    cursor(1, 1)
+    # Examples in comments use double quotes.
+    skip = "getline('.') =~ '\"'"
+    # Avoid examples that contain: "} else
+    lnum = search('[^"]}\s*else', '', 0, 0, skip)
+    assert_equal(0, lnum, fname .. ': curly before "else"')
+
+    cursor(1, 1)
+    lnum = search('else\s*{', '', 0, 0, skip)
+    assert_equal(0, lnum, fname .. ': curly after "else"')
+  endfor
+
+  bwipe!
+enddef
+
+
+" vim: shiftwidth=2 sts=2 expandtab