SQLiteConn: Add 'Raw' method to give access to underlying sqlite3 context structure

[gwd]

This is necessary, for instance, to allow users of the package to make their own CGo callbacks, and have the underlying sqlite3 library call those C functions directly.

Note that the intention from the sqlite3 library seems to be that there should be a measure of binary compatibility between versions: even extensions compiled against an older different version of sqlite3 should be able to call sqlite3_create_function with no problems. So this should work even if users of the package have a slightly different version of the sqlite3.h header.

Note that the code itself was written by @rittneje. I tested it and wrote the comments.

Signed-off-by: George Dunlap [email protected]

v2: Just copy @rittneje's code exactly:

• Grab the lock while the function is running
• Replace the error code with our own if it's of type ErrNo