Bjoin — join source buffer into destination buffer
Join destination buffer in dest with source buffer src values based on matching fields and occurrence. Function will update existing fields from source buffer to destination with matching occurrences. If field does not exist or occurrence does not exists, then field/occurrence will be removed (doing Bdel(3)).
On success, Bjoin() return zero; on error, -1 is returned, with Berror set to indicate the error.