Combine ftdetect files in a predictable order (#461)

Bash expands patterns to an alphabetically sorted list of filenames, but
the order depends on LC_COLLATE. On both Linux and BSD, `sort -V` uses
the C locale.

build

@@ -72,8 +72,11 @@ extract() {
       continue
     fi
 
-    [ -d "${dir}${subtree:-/}ftdetect" ] && for f in "${dir}${subtree:-/}ftdetect/"*; do
-      cat <<EOF >> tmp/polyglot.vim
+    ftdetect=("${dir}${subtree:-/}ftdetect"/*)
+    if [ "$ftdetect" ] && [ "$ftdetect" != "${dir}${subtree:-/}ftdetect/*" ]; then
+      IFS=$'\n' ftdetect=($(sort -V <<< "${ftdetect[*]}")); unset IFS
+      for f in "${ftdetect[@]}"; do
+        cat <<EOF >> tmp/polyglot.vim
 if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, '${pack%%:*}') == -1
   augroup filetypedetect
   " ${pack%%:*}, from ${f##*/ftdetect/} in ${pack#*:}
@@ -82,7 +85,8 @@ $(cat "${f}")
 endif
 
 EOF
-    done
+      done
+    fi
 
   done