Fixing #230; add a scrollbar to the PM popup dialog if necessary. This wasn't as easy as I thought. Had to wrap the PM text in a div with its styling (max-height and overflow). If I then resized the dialog, I'd get two scrollbars. So for now, made the dialog non-resizable.

"""
This file contains the admin definitions for the donations application.
"""
from django.contrib import admin
from donations.models import Donation

class DonationAdmin(admin.ModelAdmin):
    raw_id_fields = ('user', )

admin.site.register(Donation, DonationAdmin)