[En-Nut-Discussion] support for SD-HC cards

[PragmaLab]

> > Is SDHC support already commited?
> > I've recently tested a Trancend 4G Micro-SD without success.
> > But I'd used 4.6.3 to test and not the development branch.
> 
> Sorry, I did not get the patch...

I'm sorry too. I'll send the files to Ole asap. Have to remove some debug
lines first. 

Please note that mounting a 4GB card takes minutes using the current NutOS
fs (counting free clusters). I've modified the code to 

1) count free clusters in a more effective way (FAT16/FAT32) and 

2) only start counting free clusters when you need to know this number: just
before the first time you want to write to the card, not when mounting the
card.

Not sure if everbody likes 2), for our application it works fine since we
are writing to the card at night when counting clusters will bother nobody.
Delayed or not, there comes a moment you'll have to count the free clusters.
It is just that when inserting a card, you don't want to wait for it since
in most cases you're going to read from the card, not write. 

I'll send those 2 files as well to Ole.

Regards,

Rob