[pdftex] auto letter spacing

[Taco Hoekwater]

Hi Thanh,

>>However I am not sure the "more right" way to do this is that
>>each character c should have a kern of 5*width_of_c/1000 at
>>each side, ie the kern inserted around each character is
>>proportional to its width, instead of having a fixed global
>>value for all characters. This is more closed to the way font
>>expansion is done, but is different from what fontinst does
>>for letter-spacing.

I am much in favour of the equal width solution.