Minor changes to msn functions.

Fixed a potential error when using genclone objects in bruvo.msn
Shifted a few lines of code around to simplify conditionals and prepare for in development changes.
Modified the MSN functions to support better mlg.filter support.

All MSN functions now convert genind objects to genclone before processing.
This change should be entirely transparent to the end user, aside from allowing accurate population tracking when mlg.filter is used.