Refactor dba_(p)open() to be more sensible

[Girgias]

Actually use ZPP
Throw ValueErrors for invalid values

[cmb69]

Hmm, not sure if we can do that for BC reasons; I guess there may be custom handlers out there.

[nikic]

Generally looks fine

[nikic]

Hmm, not sure if we can do that for BC reasons; I guess there may be custom handlers out there.

It doesn't look like it's possible to register a custom handler, the list is hardcoded.

[cmb69]

It doesn't look like it's possible to register a custom handler, the list is hardcoded.

I can imagine that some customize this. However, if we document the change, we should be good.

[Girgias]

I've tested on a couple more drivers, and found a memory leak in the TokyoCabinet driver which I need to backport to 7.4 and above.

The only drivers I haven't tested the changes on now are dbm, ndmb, db2, db3, and qdbm, mainly as according to the PHP docs (which who knows if are accurate) these drivers conflict between each other and gdbm.

[nikic]

Maybe we can enable more dba handlers in CI (the ones that don't conflict)?

[Girgias]

Maybe we can enable more dba handlers in CI (the ones that don't conflict)?

I'll to figure this out, need to find the Ubuntu dependencies as I'm running on Fedora. Will make this as a separate PR I think