[Sqlalchemy-tickets] Issue #4260: PGDialect should support native decimal (zzzeek/sqlalchemy)

[pachewise <iss...@bi...>]

New issue 4260: PGDialect should support native decimal
https://bitbucket.org/zzzeek/sqlalchemy/issues/4260/pgdialect-should-support-native-decimal

pachewise:

supports_native_decimal is set to False by default, but postgres (and dialects derived from it, like Vertica) has support for Decimal/Numeric. I submitted a PR for the particular dialect we use at work (https://github.com/LocusEnergy/sqlalchemy-vertica-python/pull/18), but thought it made sense to propose the change here, too.

Test case: 
```
>> import decimal; decimal.Decimal(float(-6054546742273406781))
Decimal('-6054546742273406976')
```
(0) Have a table with a Decimal(19, 0) or Numeric(19, 0) column (or any precision > 16)
(1) Add a value like -6054546742273406781, which uses all the sig figs
(2) Do a select on that table; you'll see an SAWarning regarding decimal -> float conversion, and precision loss when it comes back as Decimal (-6054546742273406976)

using Ubuntu 14.04.5, Python 2.7.12