bot: use optionxform()-ed setting names for existence check

[dgw]

Description

This makes the "setting is defined in section" check case-insensitive, which matches the parsing behavior of RawConfigParser.

The ip plugin has a GeoIP_db_path setting that will erroneously warn users who set it using sopel-plugins configure, because the parser writes out its normalized names (in this case, geoip_db_path) and then the previous check using hasattr() wouldn't find the normalized name.

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
• I have tested the functionality of the things this change touches
  • GeoIP_db_path, geoip_db_path, and i_dont_exist settings under the [ip] section all behaved as expected (respectively: silent, silent, warning).

Notes

Trivial to backport onto 7.1.x (I've already test-cherry-picked the commit locally; no conflicts), so might as well include it in the upcoming maintenance release we already plan to make.

A nicer future solution could be overriding StaticSection.__getattr__() to just always be case insensitive—but such a big change wouldn't fly in a maintenance release.

[Exirel]

Fancy set-comprehension you got here my friend.

[dgw]

Oh yeah, I'll have to make that not-a-set-comprehension for py2 when I backport this 😑 Or maybe not, since set comprehensions should work in any 3.x and in 2.7.