move pack to correct folder if already existing but on different type (opt/start)

[melantronica]

If a minpac#add() call was changed to use a pack inside 'opt' instead 'start' it was resulting in having 2 copies of the pack. With this patch it will simply be moved to the path specified.

The regex specifying the path to be substituted could catch false positives if g:minpac#opt.minpac_start_dir would contain multiple occurrences of '/start/' or '/opt/'.

[k-takata]

Sorry for the very late response.

Could you explain why you added --recurse-submodules?
The option is relatively new and only available with 2.13 or later. https://stackoverflow.com/a/4438292/4570471
So I want to avoid using the option. (e.g. Ubuntu 16.04 comes with Git 2.7.4)
Currently, minpac executes git submodule update --init --recursive after git clone or git pull.

[melantronica]

Most likely I have overseen the implementation in the callback.
After rechecking, I agree with you. Its redundant.

[k-takata]

I have merged this into the devel branch.

[k-takata]

I have released v2.0 which includes the first commit of this PR.