patch 9.0.1106: not all postfix files are recognized

Problem:    Not all postfix files are recognized.
Solution:   Recognize main.cf.proto files. (closes #11732)

runtime/filetype.vim

@@ -1498,7 +1498,7 @@ au BufNewFile,BufRead *.plp			setf plp
 au BufNewFile,BufRead *.po,*.pot		setf po
 
 " Postfix main config
-au BufNewFile,BufRead main.cf			setf pfmain
+au BufNewFile,BufRead main.cf,main.cf.proto	setf pfmain
 
 " PostScript (+ font files, encapsulated PostScript, Adobe Illustrator)
 au BufNewFile,BufRead *.ps,*.pfa,*.afm,*.eps,*.epsf,*.epsi,*.ai	  setf postscr

src/testdir/test_filetype.vim

@@ -420,7 +420,7 @@ let s:filename_checks = {
     \ 'pdf': ['file.pdf'],
     \ 'perl': ['file.plx', 'file.al', 'file.psgi', 'gitolite.rc', '.gitolite.rc', 'example.gitolite.rc', '.latexmkrc', 'latexmkrc'],
     \ 'pf': ['pf.conf'],
-    \ 'pfmain': ['main.cf'],
+    \ 'pfmain': ['main.cf', 'main.cf.proto'],
     \ 'php': ['file.php', 'file.php9', 'file.phtml', 'file.ctp', 'file.phpt', 'file.theme'],
     \ 'pike': ['file.pike', 'file.pmod'],
     \ 'pilrc': ['file.rcp'],

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1106,
 /**/
     1105,
 /**/