patch 9.0.0006: not all Visual Basic files are recognized

Problem:    Not all Visual Basic files are recognized.
Solution:   Change detection of *.cls files. (Doug Kearns)

runtime/autoload/dist/ft.vim

@@ -72,22 +72,35 @@ export def FTbas()
 
   # most frequent FreeBASIC-specific keywords in distro files
   var fb_keywords = '\c^\s*\%(extern\|var\|enum\|private\|scope\|union\|byref\|operator\|constructor\|delete\|namespace\|public\|property\|with\|destructor\|using\)\>\%(\s*[:=(]\)\@!'
-  var fb_preproc  = '\c^\s*\%(#\a\+\|option\s\+\%(byval\|dynamic\|escape\|\%(no\)\=gosub\|nokeyword\|private\|static\)\>\)'
+  var fb_preproc  = '\c^\s*\%(' ..
+                      # preprocessor
+                      '#\s*\a\+\|' ..
+                      # compiler option
+                      'option\s\+\%(byval\|dynamic\|escape\|\%(no\)\=gosub\|nokeyword\|private\|static\)\>\|' ..
+                      # metacommand
+                      '\%(''\|rem\)\s*\$lang\>\|' ..
+                      # default datatype
+                      'def\%(byte\|longint\|short\|ubyte\|uint\|ulongint\|ushort\)\>' ..
+                    '\)'
   var fb_comment  = "^\\s*/'"
+
   # OPTION EXPLICIT, without the leading underscore, is common to many dialects
   var qb64_preproc = '\c^\s*\%($\a\+\|option\s\+\%(_explicit\|_\=explicitarray\)\>\)'
 
-  var lines = getline(1, min([line("$"), 100]))
-
-  if match(lines, fb_preproc) > -1 || match(lines, fb_comment) > -1 || match(lines, fb_keywords) > -1
-    setf freebasic
-  elseif match(lines, qb64_preproc) > -1
-    setf qb64
-  elseif match(lines, ft_visual_basic_content) > -1
-    setf vb
-  else
-    setf basic
-  endif
+  for lnum in range(1, min([line("$"), 100]))
+    var line = getline(lnum)
+    if line =~ ft_visual_basic_content
+      setf vb
+      return
+    elseif line =~ fb_preproc || line =~ fb_comment || line =~ fb_keywords
+      setf freebasic
+      return
+    elseif line =~ qb64_preproc
+      setf qb64
+      return
+    endif
+  endfor
+  setf basic
 enddef
 
 export def FTbtm()
@@ -126,6 +139,23 @@ export def FTcfg()
   endif
 enddef
 
+export def FTcls()
+  if exists("g:filetype_cls")
+    exe "setf " .. g:filetype_cls
+    return
+  endif
+
+  if getline(1) =~ '^%'
+    setf tex
+  elseif getline(1)[0] == '#' && getline(1) =~ 'rexx'
+    setf rexx
+  elseif getline(1) == 'VERSION 1.0 CLASS'
+    setf vb
+  else
+    setf st
+  endif
+enddef
+
 export def FTlpc()
   if exists("g:lpc_syntax_for_c")
     var lnum = 1