Add information about error "can't adapt type 'Decimal'" to documentation

[dmkurilov]

When you use Django with Apache and mod_wsgi (as described ​here) and when your application uses PostgreSQL with psycopg2 sometimes you get error ProgrammingError: can't adapt type 'Decimal'.

​Here and ​here is decision. I guess it would be nice to read about this error and ways to solve it in Django documentation rather than use Google.

Thanks.

[Gabriel Hurley]

There may be a useful tidbit Django could share here, but I'd like to see any potential patch have an explanation of why either the process_group directive or daemon mode setting prevent this Decimal value from being passed in erroneously. Moreover, the threads linked recommend upgrading psycopg2 and mod_wsgi; is there some minimum version required for this fix to work? Simply saying "if you're getting this error then do this" doesn't seem like enough to me.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Tim Graham]

This was fixed in psycopg 2.4.3 (ticket ​#52).