[Bizgres-general] Another loader bug fix

[Alon Goldshuv]

Well, this is not really a bug, but just something that was missing. Should
be included the upcoming release.

There were several people that were getting the following message from the
loader:

"LOADER ERROR: An error occurred while trying to send the COPY command."
Occasionally it was followed by a JVM crash...

So:

1. The bug fix I put in few days ago should take care of the JVM crash.

2. The code I committed today will append the backend error to the above
error from the loader, and the reason for failure to start COPY will be
clear. Note that this is usually a user error that will cause this. The
loader tries one pass of verifying the syntax and correctness of the LOAD
command. It then translates it to a COPY command that is sent to the
backend. In some cases the backend will reject the COPY command b/c of an
error that the loader failed to catch earlier. This error will now be
displayed, and could be fixed by the user in most cases.

Alon.