Data.clone gets a bad stylesheet

[gb119]

Steps to reproduce:
from Stoner import Data
d=Data(np.ones((2,2)),setas="xy")
d.plot()
os,chdir("/tmp")
e=d.clone

Reports that it can't find the stylesheet in the the template because the path stored in the template class is relative.

[gb119]

Fixed in 507f1e0 with more liberal use of realpath()