Improved copying from Edit Data Grid - rough patch

Hello,

I want to get involved in helping polish the pgAdmin interface. As a
first step, I've modified the copy for the Edit Data grid to have much
more flexiblity in copying data from the grid. The present code only
allows copying entire rows. With my changes, you can now copy rows,
columns, or the highlighted range.

The attached patch is very rough. The most notable rough spot is it
creates two new overloaded versions of sqlTable::GetExportLine which
duplicate a lot of code from the original. These can definitely be
consolidated, however, I wasn't sure what the preferred style would be
for it.

The next thing I would like to after finishing this is modify the query
windows to display the results in a grid instead of a list. The ability
to copy arbitrary sections of the results would be a huge help in my
daily work. I figured this could would most likely be reusable for that
goal.

Feedback would be appreciated.

Ed