patch 8.2.2879: file extension .hsig not recognized

Problem:    File extension .hsig not recognized.
Solution:   Use Haskell filetype for .hsig files. (Marcin Szamotulski,
            closes #8236)

Author: coot

runtime/filetype.vim

@@ -718,7 +718,7 @@ au BufNewFile,BufRead *.haml			setf haml
 au BufNewFile,BufRead *.hsm			setf hamster
 
 " Haskell
-au BufNewFile,BufRead *.hs,*.hsc,*.hs-boot	setf haskell
+au BufNewFile,BufRead *.hs,*.hsc,*.hs-boot,*.hsig setf haskell
 au BufNewFile,BufRead *.lhs			setf lhaskell
 au BufNewFile,BufRead *.chs			setf chaskell
 au BufNewFile,BufRead cabal.project		setf cabalproject

src/testdir/test_filetype.vim

@@ -211,7 +211,7 @@ let s:filename_checks = {
     \ 'gtkrc': ['.gtkrc', 'gtkrc', '.gtkrc-file', 'gtkrc-file'],
     \ 'haml': ['file.haml'],
     \ 'hamster': ['file.hsm'],
-    \ 'haskell': ['file.hs', 'file.hsc', 'file.hs-boot'],
+    \ 'haskell': ['file.hs', 'file.hsc', 'file.hs-boot', 'file.hsig'],
     \ 'haste': ['file.ht'],
     \ 'hastepreproc': ['file.htpp'],
     \ 'hb': ['file.hb'],

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2879,
 /**/
     2878,
 /**/