Cleaning up m2-snapshot-repository

[Matt Hogstrom]

I am deploying the 2.1-SNAPSHOT from trunk this morning and while  
verifying the file permissions I noticed the old -Mn SNAPSHOTs.  If  
no one has any objections I'll clean up all SNAPSHOTs up to (and not  
including) M6 to be a little more efficient on space.

Let me know if you object or have concerns.