Improvements in Copy From

Hi,

While reviewing copy from I identified few  improvements for copy from
that can be done :
a) copy from stdin copies lesser amount of data to buffer even though
space is available in buffer because minread was passed as 1 to
CopyGetData, Hence it only reads until the data read from libpq is
less than minread. This can be fixed by passing the actual space
available in buffer, this reduces the unnecessary frequent calls to
CopyGetData.
b) CopyMultiInsertInfoNextFreeSlot had an unused function parameter
that is not being used, it can be removed.
c) Copy from reads header line and do nothing for the header line, we
need not clear EOL & need not convert to server encoding for the
header line.

Attached patch has the changes for the same.
Thoughts?

Regards,
Vignesh
EnterpriseDB: http://www.enterprisedb.com