patch 8.0.0423: changing 'cinoptions' does not always work

Problem:    The effect of adding "#" to 'cinoptions' is not always removed.
            (David Briscoe)
Solution:   Reset b_ind_hash_comment. (Christian Brabandt, closes #1475)

src/testdir/Make_all.mak

@@ -143,6 +143,7 @@ NEW_TESTS = test_arabic.res \
 	    test_cdo.res \
 	    test_channel.res \
 	    test_charsearch.res \
+	    test_cindent.res \
 	    test_cmdline.res \
 	    test_command_count.res \
 	    test_crypt.res \

src/testdir/test3.in

@@ -1,6 +1,7 @@
 /* vim: set cin ts=4 sw=4 : */
 
-Test for 'cindent'
+Test for 'cindent'.
+For new tests, consider putting them in test_cindent.vim.
 
 STARTTEST
 :so small.vim

src/testdir/test_cindent.vim

@@ -0,0 +1,16 @@
+" Test for cinoptions and cindent
+"
+" TODO: rewrite test3.in into this new style test
+
+func Test_cino_hash()
+  " Test that curbuf->b_ind_hash_comment is correctly reset
+  new
+  setlocal cindent cinoptions=#1
+  setlocal cinoptions=
+  call setline(1, ["#include <iostream>"])
+  call cursor(1, 1)
+  norm! o#include
+  "call feedkeys("o#include\<esc>", 't')
+  call assert_equal(["#include <iostream>", "#include"], getline(1,2))
+  bwipe!
+endfunc