[Proj] Error code for PJD_ERR_GEOCENTRIC and pj_strerrno()

[proj-admin at remotesensing.org]

Hi all,

According to the documentation, errors detected by libproj itself should
always
have negative numbers, whereas errors in system libraries have positive.
I recently got error number 100, which turned out to be the following error,
defined in projects.h:

    /* datum system errors */
    #define PJD_ERR_GEOCENTRIC 100

Is there a reason this error doesn't follow the strategy of the other
errors,
and that it isn't "known" by pj_strerrno().

Regards
Thomas