proposal - get_extension_version function

[Pavel Stehule]

Hi

I try to write a safeguard check that ensures the expected extension
version for an extension library.

Some like

const char *expected_extversion = "2.5";

...

extoid = getExtensionOfObject(ProcedureRelationId, fcinfo->flinfo->fn_oid));
extversion = get_extension_version(extoid);
if (strcmp(expected_extversion, extversion) != 0)
   elog(ERROR, "extension \"%s\" needs \"ALTER EXTENSION %s UPDATE\",
          get_extension_name(extversion),
          get_extension_name(extversion)))

Currently the extension version is not simply readable - I need to read
directly from the table.

Notes, comments?

Regards

Pavel