Avoid detecting exfat-utils commands as exfatprogs commands

Fix for issue #137 (closed) "Creating exfat partition with a label fails with error"

Partial quote from the commit message:

A user had exfat-utils installed and tried to use GParted to create an
exfat file system.  GParted ran this command but it failed:
    # mkfs.exfat -L '' '/dev/sdb1'
    mkexfatfs 1.3.0
    mkfs.exfat: invalid option -- 'L'
    Usage: mkfs.exfat [-i volume-id] [-n label] [-p partition-first-sector] [-s sectors-per-cluster] [-V] <device>

The problem is that both exfat-utils and exfatprogs packages provide
mkfs.exfat and fsck.exfat commands but they have incompatible command
line options and GParted is programmed for exfatprogs.  So far GParted
just checks the executable exists, hence the mis-identification.