Support oid query and necassary types

[michalmuskala]

Example: SELECT typname FROM pg_type WHERE oid = …;

\cc @ericmj

[ericmj]

We should try to support the types of all columns in the pg_type table.

[fishcakez]

Apart from the char type, which can be handled by raw extension as a string of single codepoint, I think the other types can only use the text format but do not make sense as text (aclitem, _aclitem, pg_node_tree). Should we add support for char and require the others to be cast as text?

[fishcakez]

I've added support for the special "char" type, I think the others only have text format. @ericmj @michalmuskala could you please check what types you'd like support for.

[ericmj]

If they are text only there isn't much we can do unfortunately. I think we can close this for now.