usalc and lmsalc (salt content)

In ocean pp there appears to be a bug in the 2 functions that calculate salt content between 0-300 m (usalc) and 300m-bottom (lmsalc). Apparently the two functions are switched, so one calculates the result of the other. I corrected it here /home/eexarchou/ocean_diagnostics/ocean_pp.bash or alternatively, it is in the branch develop-testeleftheria So one could check it @pabretonniere @vguemas

Cheers Eleftheria