Reuse geometry for back-edge when geometry is reversed.

This should address #1511.

Results for an example street-data only graph:
         Graph size
         (mem)      (disk)     Gain %
    A    117502000  50288000
    B    111162000  45280965   5.4%
    (number of StreetEdge 354071)

A - Original version
B - With shared reversed geometry

More simply, this method could be replaced by the standard standard library Arrays.equals(int[], int[]). It's a bit funny, Eclipse auto-completion did not proposed it to me in the first place.