[PATCH] Slight improvement of worker_spi.c example

Hi,

Currently the example uses the following order of calls:

StartTransactionCommand();
SPI_connect();
PushActiveSnapshot(...);

...

SPI_finish();
PopActiveSnapshot();
CommitTransactionCommand();

This could be somewhat misleading. Typically one expects something to be freed
in a reverse order compared to initialization. This creates a false impression
that PushActiveSnapshot(...) _should_ be called after SPI_connect().

The patch changes the order to:

StartTransactionCommand();
PushActiveSnapshot(...);
SPI_connect();

...

SPI_finish();
PopActiveSnapshot();
CommitTransactionCommand();

... and also clarifies that the order of PushActiveSnapshot(...) and
SPI_connect() is not important.

--
Best regards,
Aleksander Alekseev