fix missing postscript preamble when -Tps follows some other format, e.g: 	dot hello.dot -Tpng:pango -o hello.png -Tps:core -o hello.ps
fix missing postscript preamble when -Tps follows some other format, e.g:
	dot hello.dot -Tpng:pango -o hello.png -Tps:core -o hello.ps

MjAbuz/graphviz,pixelglow/graphviz,BMJHayward/graphviz,ellson/graphviz,BMJHayward/graphviz,kbrock/graphviz,tkelman/graphviz,jho1965us/graphviz,jho1965us/graphviz,jho1965us/graphviz,jho1965us/graphviz,tkelman/graphviz,jho1965us/graphviz,MjAbuz/graphviz,tkelman/graphviz,MjAbuz/graphviz,jho1965us/graphviz,pixelglow/graphviz,MjAbuz/graphviz,tkelman/graphviz,MjAbuz/graphviz,jho1965us/graphviz,BMJHayward/graphviz,pixelglow/graphviz,pixelglow/graphviz,MjAbuz/graphviz,pixelglow/graphviz,kbrock/graphviz,kbrock/graphviz,ellson/graphviz,kbrock/graphviz,ellson/graphviz,pixelglow/graphviz,BMJHayward/graphviz,ellson/graphviz,BMJHayward/graphviz,kbrock/graphviz,tkelman/graphviz,kbrock/graphviz,pixelglow/graphviz,tkelman/graphviz,ellson/graphviz,BMJHayward/graphviz,kbrock/graphviz,pixelglow/graphviz,BMJHayward/graphviz,MjAbuz/graphviz,BMJHayward/graphviz,kbrock/graphviz,ellson/graphviz,ellson/graphviz,tkelman/graphviz,ellson/graphviz,pixelglow/graphviz,tkelman/graphviz,pixelglow/graphviz,jho1965us/graphviz,MjAbuz/graphviz,BMJHayward/graphviz,ellson/graphviz,BMJHayward/graphviz,ellson/graphviz,jho1965us/graphviz,MjAbuz/graphviz,jho1965us/graphviz,pixelglow/graphviz,ellson/graphviz,MjAbuz/graphviz,kbrock/graphviz,BMJHayward/graphviz,kbrock/graphviz,kbrock/graphviz,MjAbuz/graphviz,tkelman/graphviz,tkelman/graphviz,tkelman/graphviz,jho1965us/graphviz