Ert 795 and 799

ERT 795: Insufficient number of decimals outputted in parameters.txt: 
Changed printf format from %e to %g in method en_kw_write_export_file(...)

ERT_799: For parameters that are logarithmically distributed in the prior (as given to GEN_KW), the logarithm of the value should also be printed to 'parameters.txt':
Added printing of the logarithm of the value in method en_kw_write_export_file(...)

Added test to verify printout of logarithm of the value when the prior is logarithmically distributed