Allow negative values for aasqueeze

[Tux]

A negative value will add extra whitespace between the lines, which may serve two purposes: if a font has descenders that don't show for aasqueeze=0, like the '_' character, setting aasqueeze to -2 might make it visible. The other purpose might be simulating double line-height in presentations by choosing a high negative value like aasqueeze=-10

Signed-off-by: H.Merijn Brand - Tux linux@tux.freedom.nl

[mbert]

I cannot really test this since I don't have a Linux machine at hand. If anybody runs into problems with it, please report.