Fix SQLAlchemy 0.9.x compatibility

[jank]

Build with SQLAlchemy 0.9.x fails. Go through the change log and migration guide to determine what is necessary to support 0.8.x and 0.9.x in parallel:

http://docs.sqlalchemy.org/en/rel_0_9/changelog/migration_09.html
http://docs.sqlalchemy.org/en/latest/changelog/changelog_09.html

[jank]

Done several fixes to get to 0.9.4 support. The test suite covers more aspects of the dialect and uncovered some glitches in identifier preparing (identifiers with leading _ were not quoted, retrieval of the row_id was incorrect). Waiting for one pull request to be merged and released with sqla:
zzzeek/sqlalchemy#95
String test incorrectly references Text type.

[jank]

Switching to 0.9.x requires to switch to py.test. Support for py.test was only added with 0.9. Hence, 0.8 cannot be supported anymore. All users must upgrade to sqla 0.9

[jank]

Done, nose test support removed. No test for 0.8.x possible.