patch 9.1.0731: inconsistent case sensitive extension matching

Problem:  inconsistent case sensitive extension matching
Solution: unify case sensitive extension matching (Evgeni Chasnovski).

There are different approaches of how extensions are matched with
respect to case sensitivity. In particular, '\c' flag is used in pattern
whereas in most places case sensitive matching is guarded behind
`has("fname_case")` condition.

Replace all instances of '\c' with an explicit case sensitive pattern
variants guarded by `has("fname_case")`. Strictly speaking, this is a
breaking change because only two (most common and prevailingly tested)
variants are now matched: upper first letter and upper all letters.

closes: #15672

Signed-off-by: Evgeni Chasnovski <evgeni.chasnovski@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/filetype.vim b/runtime/filetype.vim
index 3af6d03..3441518 100644
--- a/runtime/filetype.vim
+++ b/runtime/filetype.vim
@@ -237,7 +237,10 @@
 au BufNewFile,BufRead *.cmd
 	\ if getline(1) =~ '^/\*' | setf rexx | else | setf dosbatch | endif
 " ABB RAPID or Batch file for MSDOS.
-au BufNewFile,BufRead *.sys\c			call dist#ft#FTsys()
+au BufNewFile,BufRead *.sys			call dist#ft#FTsys()
+if has("fname_case")
+  au BufNewFile,BufRead *.Sys,*.SYS			call dist#ft#FTsys()
+endif
 
 " Batch file for 4DOS
 au BufNewFile,BufRead *.btm			call dist#ft#FTbtm()
@@ -455,7 +458,10 @@
 au BufNewFile,BufRead .cling_history		setf cpp
 
 " Clipper, FoxPro, ABB RAPID or eviews
-au BufNewFile,BufRead *.prg\c			call dist#ft#FTprg()
+au BufNewFile,BufRead *.prg			call dist#ft#FTprg()
+if has("fname_case")
+  au BufNewFile,BufRead *.Prg,*.PRG			call dist#ft#FTprg()
+endif
 
 " Clojure
 au BufNewFile,BufRead *.clj,*.cljs,*.cljx,*.cljc		setf clojure
@@ -602,7 +608,10 @@
 au BufNewFile,BufRead .wakatime.cfg		setf dosini
 
 " Configure files
-au BufNewFile,BufRead *.cfg\c			call dist#ft#FTcfg()
+au BufNewFile,BufRead *.cfg			call dist#ft#FTcfg()
+if has("fname_case")
+  au BufNewFile,BufRead *.Cfg,*.CFG			call dist#ft#FTcfg()
+endif
 
 " Cucumber
 au BufNewFile,BufRead *.feature			setf cucumber
@@ -1227,9 +1236,14 @@
 au BufNewFile,BufRead *.kix			setf kix
 
 " Kuka Robot Language
-au BufNewFile,BufRead *.src\c			call dist#ft#FTsrc()
-au BufNewFile,BufRead *.dat\c			call dist#ft#FTdat()
-au BufNewFile,BufRead *.sub\c			setf krl
+au BufNewFile,BufRead *.src			call dist#ft#FTsrc()
+au BufNewFile,BufRead *.dat			call dist#ft#FTdat()
+au BufNewFile,BufRead *.sub			setf krl
+if has("fname_case")
+   au BufNewFile,BufRead *.Src,*.SRC			call dist#ft#FTsrc()
+   au BufNewFile,BufRead *.Dat,*.DAT			call dist#ft#FTdat()
+   au BufNewFile,BufRead *.Sub,*.SUB			setf krl
+endif
 
 " Kimwitu[++]
 au BufNewFile,BufRead *.k			setf kwt
@@ -1479,7 +1493,10 @@
 au BufNewFile,BufRead *.mmp			setf mmp
 
 " ABB Rapid, Modula-2, Modsim III or LambdaProlog
-au BufNewFile,BufRead *.mod\c			call dist#ft#FTmod()
+au BufNewFile,BufRead *.mod			call dist#ft#FTmod()
+if has("fname_case")
+   au BufNewFile,BufRead *.Mod,*.MOD			call dist#ft#FTmod()
+endif
 
 " Modula-3 (.m3, .i3, .mg, .ig)
 au BufNewFile,BufRead *.[mi][3g]		setf modula3
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index c10023d..45a5df2 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -1155,15 +1155,14 @@
   unlet g:filetype_cfg
 
   " RAPID cfg
-  let ext = 'cfg'
   for i in ['EIO', 'MMC', 'MOC', 'PROC', 'SIO', 'SYS']
-    call writefile([i .. ':CFG'], 'cfgfile.' .. ext)
-    execute "split cfgfile." .. ext
-    call assert_equal('rapid', &filetype)
-    bwipe!
-    call delete('cfgfile.' .. ext)
-    " check different case of file extension
-    let ext = substitute(ext, '\(\l\)', '\u\1', '')
+    for ext in ['cfg', 'Cfg', 'CFG']
+      call writefile([i .. ':CFG'], 'cfgfile.' .. ext)
+      execute "split cfgfile." .. ext
+      call assert_equal('rapid', &filetype)
+      bwipe!
+      call delete('cfgfile.' .. ext)
+    endfor
   endfor
 
   " clean up
diff --git a/src/version.c b/src/version.c
index 4f6375b..a2d6bfd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    731,
+/**/
     730,
 /**/
     729,