Make routine for reading of Xcompact files faster

[joneuhauser]

Reading a restart file takes ~50s on my system, which is the main bottleneck of the FTLE computation. (Compared to this, reading the file in Numpy takes about 2 seconds).
The relevant code:

activeBarriers/aftle/xCompactInterface.cpl

Lines 30 to 36 in f76bc1c

	diskfield=OPEN(field_name)
	WITH diskfield:
	LOOP FOR iV=0 TO 2 AND iz=0 TO nzd-1
	ARRAY(0..ny, 0..nxd-1) OF REAL buf = fieldimage(iV,iz,*,*);
	DO V(ix,iz,iy,iV) = buf(iy,ix) FOR iy=0 TO ny AND ix=0 TO nxd-1
	REPEAT
	CLOSE diskfield

[davecats]

@jhofinger Are you comparing both reading (in numpy and with the FLTE program) on the same computer? One reason for the slowness could be that I am not reading the whole file contiguously (as you see I am doing some index permutation while reading). At the cost of a little further memory I could read the whole field and do the permutation in memory.

I could implement the two option with could be switched via a compile-time macro #define readContiguous