patch 9.0.0779: lsl and lm3 file extensions are not recognized

Problem:    lsl and lm3 file extensions are not recognized.
Solution:   Add *.lsl and *.lm3 patterns. (Doug Kearns, closes #11384)

runtime/autoload/dist/ft.vim

@@ -1087,5 +1087,18 @@ export def FTdat()
   endif
 enddef
 
+export def FTlsl()
+  if exists("g:filetype_lsl")
+    exe "setf " .. g:filetype_lsl
+  endif
+
+  var line = getline(nextnonblank(1))
+  if line =~ '^\s*%' || line =~# ':\s*trait\s*$'
+    setf larch
+  else
+    setf lsl
+  endif
+enddef
+
 # Uncomment this line to check for compilation errors early
 # defcompile

runtime/doc/filetype.txt

@@ -150,6 +150,7 @@ variables can be used to overrule the filetype used for certain extensions:
 	*.fs		g:filetype_fs	|ft-forth-syntax|
 	*.i		g:filetype_i	|ft-progress-syntax|
 	*.inc		g:filetype_inc
+	*.lsl		g:filetype_lsl
 	*.m		g:filetype_m	|ft-mathematica-syntax|
 	*.mod		g:filetype_mod
 	*.p		g:filetype_p	|ft-pascal-syntax|

runtime/filetype.vim

@@ -1032,6 +1032,9 @@ au BufNewFile,BufRead Kconfig,Kconfig.debug	setf kconfig
 " Lace (ISE)
 au BufNewFile,BufRead *.ace,*.ACE		setf lace
 
+" Larch Shared Language
+au BufNewFile,BufRead .lsl			call dist#ft#FTlsl()
+
 " Latexmkrc
 au BufNewFile,BufRead .latexmkrc,latexmkrc	setf perl
 
@@ -1122,7 +1125,7 @@ au BufNewFile,BufRead .luacheckrc		setf lua
 au BufNewFile,BufRead *.rockspec		setf lua
 
 " Linden Scripting Language (Second Life)
-au BufNewFile,BufRead *.lsl			setf lsl
+au BufNewFile,BufRead *.lsl			call dist#ft#FTlsl()
 
 " Lynx style file (or LotusScript!)
 au BufNewFile,BufRead *.lss			setf lss
@@ -1220,6 +1223,9 @@ au BufNewFile,BufRead *.m2,*.DEF,*.mi		setf modula2
 " Modula-3 (.m3, .i3, .mg, .ig)
 au BufNewFile,BufRead *.[mi][3g]		setf modula3
 
+" Larch/Modula-3
+au BufNewFile,BufRead *.lm3			setf modula3
+
 " Monk
 au BufNewFile,BufRead *.isc,*.monk,*.ssc,*.tsc	setf monk