PRAGMA foreign_keys still no-op

[Zhu-jiatong]

Issue description:
After the fix proposed in #90, the "PRAGMA foreign_keys" query is still a no-op, where no data is returned. The expected result of the query is 1 after the aforementioned fix.

Expected reason:
I noticed that the #undef SQLITE_OMIT_PRAGMA line along with other PRAGMA options are commented out in the config_ext.h file. This makes it hard to check the availability of features at run-time.

Proposal:
Enable the PRAGMA command to allow for easier run-time status checks. Thank you.