dynamic clipboard types

Hi,

I'd like to implement dynamic clipboard types for components. I attach a
preliminary patch which makes things work. Note that this patch uses
std::vector.

It only works with GChemPaint at the moment, because of the other two
components I wrote, drgeo does not support clipboard operations and
gnumeric data are already pasted as a table, and I don't want to break
that, at least before it has been discussed (anyway, it would need some
hack in gnumeric).

Things work mostly like for graphics types. I saw that the file type is
retrieved using the sniffer, but we already know the mime type. I
suggest to add some map to get the correspondance between mime types and
file types, probably with a new method in the IE_ImpGraphic class.

Btw, there is a question I had in mind for some time: what are the rules
for identation, spaces and other styles in abi souce code? Seems they
are somewhat developer dependent. It's of course of minor importance,
but...

Cheers,
Jean

-- 
Jean Bréfort <jean.brefort@normalesup.org>