XP command can give fractional experience points

Using the command /xp 1L can result in having a fractional number of experience points.

Steps to reproduce:

1. Starting at 5 xp, using /xp 1L results in having between 13 and 14 xp.
2. Use /xp 2 to gain 2 xp, putting you below level 2.
3. Use /xp 1 to gain 1 xp, putting you above level 2.

What should happen:

At either step 2 or step 3, your level should be exactly 2.

What happens:

Experience level is no longer an integer.