Experimental support in VLIV for BigTIFF

I have checkout-ed this morning the libtiff CVS and compiled VLIV using this version (it's 4.0 beta I think).

This should allow BigTIFF files support.
I have tested on a few files, but did not go as far as getting large (huge, more than 4 gigabytes) files to better test.

Remember this is a giant step in supporting really large image, I cannot see a real limit other than disk space now, as a 1 Terabyte image only scratches the surface of possible file size with BigTIFF.

If you have large BigTIFF images, please test VLIV support for them and report any problem.