- The 'length' argument to all Numeric types has been renamed

- The 'length' argument to all Numeric types has been renamed
to 'scale'.  'length' is deprecated and is still accepted
with a warning. [ticket:827]
- The 'length' argument to MSInteger, MSBigInteger, MSTinyInteger,
MSSmallInteger and MSYear has been renamed to 'display_width'.
[ticket:827]
- mysql._Numeric now consumes 'unsigned' and 'zerofill' from
the given kw, so that the same kw can be passed along to Numeric
and allow the 'length' deprecation logic to still take effect
- added testlib.engines.all_dialects() to return a dialect for
every db module
- informix added to sqlalchemy.databases.__all__.  Since other
"experimental" dbs like access and sybase are there, informix
should be as well.