Make "yadm clone --recursive" work as expected (#517)

The --recursive switch was ignored when YADM clones a dotfile repository.
This commit causes "yadm clone --recursive" to also clone submodules
in one go, similar to what GIT does when given the --recursive switch.

yadm

@@ -754,6 +754,7 @@ function clone() {
   DO_BOOTSTRAP=1
   local -a args
   local -i do_checkout=1
+  local -i do_submodules=0
   while [[ $# -gt 0 ]]; do
     case "$1" in
       --bootstrap) # force bootstrap, without prompt
@@ -768,7 +769,10 @@ function clone() {
       -n | --no-checkout)
         do_checkout=0
         ;;
-      --bare | --mirror | --recurse-submodules* | --recursive | --separate-git-dir=*)
+      --recursive)
+        do_submodules=1
+        ;;
+      --bare | --mirror | --recurse-submodules* | --separate-git-dir=*)
         # ignore arguments without separate parameter
         ;;
       --separate-git-dir)
@@ -835,6 +839,10 @@ function clone() {
       "$GIT_PROGRAM" checkout -- ":/$file"
     done
 
+    if [[ $do_submodules -ne 0 ]]; then
+      "$GIT_PROGRAM" submodule update --init --recursive
+    fi
+
     if [ -n "$("$GIT_PROGRAM" ls-files --modified)" ]; then
       local msg
       IFS='' read -r -d '' msg <<EOF