Clean up pc-bootconfig a bit:
1) Prevent the user from removing/renaming the "default" BE (appears to be required by all other BE's)
2) Clean up the command execution scheme so that the wait messages show up properly.
3) Ensure that the GRUB menu is rebuilt whenever the BE list gets changed (rename, remove, new, etc..)
Merge branch 'master' of github.com:pcbsd/pcbsd