Application of Sebastien Morin's patch creating the N15_CSA and NH_BOND_LENGTH constants.
For the patch, see the post at https://mail.gna.org/public/relax-devel/2007-07/msg00060.html.
The patch 'patch__default_csa_r__l1.3_r3351' makes uniform the use of the CSA value (now -172 ppm
everywhere) and fixes the test-suite (in jw_mapping) to account for this change. It also adds two
constants for the CSA and NH bond length default values.