[Patch] LaTeX: export nested lists

Dear all,

Currently AbiWord can only export flat (single-level) lists to LaTeX
documents. This patch tries to extend this function to more complex
lists. It was diff-ed against main trunk. Although it is not perfect
and may even contain bugs, I still want to send it to the list to
gather comments and feedback.

The simple mechanism to recognize nested lists is based on their indentation.

I have also attached a test file "List_test.abw". In AbiWord, simply
save this file as a LaTeX document, then run latex on the LaTeX
document, and run xdvi to preview.

-- 
Thanks & regards
Xun Sun