eigen3 whitespace does not conform to modeline

[ryandesign (Ryan Carsten Schmidt)]

The eigen3 port uses the standard modeline, which states among other things that indentations will occur at multiples of four spaces, but the actual whitespace of the portfile uses indentations at multiples of two spaces. Either the modeline should be changed to match the reality of the portfile's whitespace, or ideally, since this is our standard modeline and the one we would prefer to use, the whitespace of the portfile should be changed to conform to the modeline.

[eborisch (Eric A. Borisch)]

Fixed in r98001.