patch 8.2.3599: not all gdbinit files are recognized

Problem:    Not all gdbinit files are recognized.
Solution:   Add "gdbinit". (Doug Kearns)

runtime/filetype.vim

@@ -647,7 +647,7 @@ au BufNewFile,BufRead *.fsl			setf framescript
 au BufNewFile,BufRead fstab,mtab		setf fstab
 
 " GDB command files
-au BufNewFile,BufRead .gdbinit			setf gdb
+au BufNewFile,BufRead .gdbinit,gdbinit		setf gdb
 
 " GDMO
 au BufNewFile,BufRead *.mo,*.gdmo		setf gdmo

src/testdir/test_filetype.vim

@@ -188,7 +188,7 @@ let s:filename_checks = {
     \ 'freebasic': ['file.fb', 'file.bi'],
     \ 'fstab': ['fstab', 'mtab'],
     \ 'fvwm': ['/.fvwm/file', 'any/.fvwm/file'],
-    \ 'gdb': ['.gdbinit'],
+    \ 'gdb': ['.gdbinit', 'gdbinit'],
     \ 'gdmo': ['file.mo', 'file.gdmo'],
     \ 'gedcom': ['file.ged', 'lltxxxxx.txt', '/tmp/lltmp', '/tmp/lltmp-file', 'any/tmp/lltmp', 'any/tmp/lltmp-file'],
     \ 'gemtext': ['file.gmi', 'file.gemini'],

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3599,
 /**/
     3598,
 /**/