get and set bounding box
currentBBox=ebbox([newBBox[,epsFileName]])
newBBox :
default: -1 = read old box coordinates of file
if a scalar then newBBox is min. distance (in eUserUnits)
between objects and then new calculated bounding box
if a vector 1x4 then newBBox are the new
bounding box coordinates [x0 y0 x1 y1] in 1/72 inchs
epsFileName :
name of eps-file
default: ‘eFileName’
currentBBox :
current Bounding Box of eps-file