clojure.java.jdbc compatibility in concurrent connection usage

[seancorfield]

Is your feature request related to a problem? Please describe.
See #244 for background.

Describe the solution you'd like
If you bind *nested-tx* to :ignore to get c.j.j compatibility there, you should also get compatibility on the (non-)locking of Connection to match c.j.j's unsafe behavior (see #106 for why that changed in the first place).

[seancorfield]

@camsaul this is on develop and in the latest 1.3.999-SNAPSHOT for testing.

[camsaul]

Thanks, I'll give it a shot tomorrow!

[camsaul]

Thanks @seancorfield, the fix works for us! 🥳