Dear list,

Attached is a patch that allows some customization of tables in LaTeX
export.

It adds three new customizable with default values:

  org-export-latex-tables-tstart : nil
  org-export-latex-tables-hline  : "\\hline"
  org-export-latex-tables-tend   : nil

These variables allows users to use e.g. the booktabs package (use
\\toprule, \\midrule and \\bottomrule for the respective variables above
- these are options you'll find in the defcustoms too) and create more
beautiful tables in LaTeX documents.

The patch also fixes the double rule after the table head when using a
longtable environment, as this 1) is ugly and 2) caused booktabs
longtables to go quite awry.

The patch does - save for the longtable fix - bring no change to the
export of existing code as long as the defaults are not changed.