…tocentric geodetic CRS

This also fixes conversion between geocentric latlong and geodetic latlong
with cs2cs. This was dealt with in PR 1093, but in the wrong direction
(the geocentric latitude must be <= in absolute value to the geodetic one)
The issue here was linked to the semantics of the +geoc specifier, which
affects the semantics of the input coordinates in the forward direction
(+geoc means that the input coordinate is is a geocentric latitude),
which defeats the logic of doing A to B by using the inverse path of A
and the forward path of B.

…ameters

… <--> geocentric latitude