Installation stops too early when vimproc is not used.

After 436e4d4c5fff7023e95d93886724adfb690f3425, the loop exit condition in `s:install()` is always true when vimproc is not used. As a result, installation will always stop after `g:neobundle#install_max_processes` bundles have been installed, even if there are still more bundles to install. I think this can also happen if, when using vimproc, all spawned processes happen to finish at the same time.