patch 9.1.1606: filetype: a few more files are not recognized

Problem:  filetype: a few more files are not recognized
Solution: guess Mail, Info and Terminfo files by its content
          (lacygoill)

closes: #17880

Signed-off-by: lacygoill <lacygoill@lacygoill.me>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_filetype.vim

@@ -3024,6 +3024,39 @@ func Test_org_file()
   filetype off
 endfunc
 
+func Test_info_file()
+  filetype on
+
+  call writefile(['File: coreutils.info,  Node: Top,  Next: Introduction,  Up: (dir)', 'D'], 'Xfile', 'D')
+  split Xfile
+  call assert_equal('info', &filetype)
+  bwipe!
+
+  filetype off
+endfunc
+
+func Test_mail_file()
+  filetype on
+
+  call writefile(['Return-path: <lgc@debian.home.arpa>', 'D'], 'Xfile', 'D')
+  split Xfile
+  call assert_equal('mail', &filetype)
+  bwipe!
+
+  filetype off
+endfunc
+
+func Test_terminfo_file()
+  filetype on
+
+  call writefile(['#	Reconstructed via infocmp from file: /etc/terminfo/x/xterm', 'D'], 'Xfile', 'D')
+  split Xfile
+  call assert_equal('terminfo', &filetype)
+  bwipe!
+
+  filetype off
+endfunc
+
 " Filetypes detected from names of existing files
 func Test_pacmanlog()
   filetype on

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1606,
 /**/
     1605,
 /**/