Change license of mb, mlprof, modulecmd, mpub, mrel, mt, mtreview,
nglfar2ccov and playdemo scripts from GPLv3+ to GPLv2+.
Align this way all files from the Modules project under the GPLv2+
license.
Consent has been obtained from copyright holder to perform such move (I
hold the full copyright for these script files).
Related to #389