patch 8.2.0988: getting directory contents is always case sorted

Problem:    Getting directory contents is always case sorted.
Solution:   Add sort options and v:collate. (Christian Brabandt, closes #6229)
diff --git a/src/proto/fileio.pro b/src/proto/fileio.pro
index 2171e6b..cdf9274 100644
--- a/src/proto/fileio.pro
+++ b/src/proto/fileio.pro
@@ -31,7 +31,7 @@
 void buf_reload(buf_T *buf, int orig_mode);
 void buf_store_time(buf_T *buf, stat_T *st, char_u *fname);
 void write_lnum_adjust(linenr_T offset);
-int readdir_core(garray_T *gap, char_u *path, int withattr, void *context, int (*checkitem)(void *context, void *item));
+int readdir_core(garray_T *gap, char_u *path, int withattr, void *context, int (*checkitem)(void *context, void *item), int sort);
 int delete_recursive(char_u *name);
 void vim_deltempdir(void);
 char_u *vim_tempname(int extra_char, int keep);