Fix pyenv#1118: follow only dir-symlinks

This corrects the deffect where pyenv tries to determine an absolute
path of the directory containing a file and follows symlinks
manually. Because of missing check it behaved correctly, but a
misleading error message was shown in the terminal output.

Thanks to @HQJaTu for the patch

libexec/pyenv

@@ -43,7 +43,7 @@ else
     while [ -n "$path" ]; do
       cd "${path%/*}"
       local name="${path##*/}"
-      path="$(resolve_link "$name" || true)"
+      path="$(test -d "$name" && resolve_link "$name" || true)"
     done
 
     pwd