patch 9.0.0012: signature files not detected properly

Problem:    Signature files not detected properly.
Solution:   Add a function to better detect signature files. (Doug Kearns)

src/testdir/test_filetype.vim

@@ -313,7 +313,6 @@ let s:filename_checks = {
     \ 'lotos': ['file.lot', 'file.lotos'],
     \ 'lout': ['file.lou', 'file.lout'],
     \ 'lpc': ['file.lpc', 'file.ulpc'],
-    \ 'lprolog': ['file.sig'],
     \ 'lsl': ['file.lsl'],
     \ 'lss': ['file.lss'],
     \ 'lua': ['file.lua', 'file.rockspec', 'file.nse'],
@@ -1760,4 +1759,59 @@ func Test_cls_file()
   filetype off
 endfunc
 
+func Test_sig_file()
+  filetype on
+
+  call writefile(['this is neither Lambda Prolog nor SML'], 'Xfile.sig')
+  split Xfile.sig
+  call assert_equal('', &filetype)
+  bwipe!
+
+  " Test dist#ft#FTsig()
+
+  let g:filetype_sig = 'sml'
+  split Xfile.sig
+  call assert_equal('sml', &filetype)
+  bwipe!
+  unlet g:filetype_sig
+
+  " Lambda Prolog
+
+  call writefile(['sig foo.'], 'Xfile.sig')
+  split Xfile.sig
+  call assert_equal('lprolog', &filetype)
+  bwipe!
+
+  call writefile(['/* ... */'], 'Xfile.sig')
+  split Xfile.sig
+  call assert_equal('lprolog', &filetype)
+  bwipe!
+
+  call writefile(['% ...'], 'Xfile.sig')
+  split Xfile.sig
+  call assert_equal('lprolog', &filetype)
+  bwipe!
+
+  " SML signature file
+
+  call writefile(['signature FOO ='], 'Xfile.sig')
+  split Xfile.sig
+  call assert_equal('sml', &filetype)
+  bwipe!
+
+  call writefile(['structure FOO ='], 'Xfile.sig')
+  split Xfile.sig
+  call assert_equal('sml', &filetype)
+  bwipe!
+
+  call writefile(['(* ... *)'], 'Xfile.sig')
+  split Xfile.sig
+  call assert_equal('sml', &filetype)
+  bwipe!
+
+  call delete('Xfile.sig')
+  filetype off
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    12,
 /**/
     11,
 /**/