Log Message:
geography/proj: Update to 5.2.0 and datumgrids 1.8

Add c++ to USE_LANGUAGES because configure throws an error.  (This
isn't noted in the release notes, but has been talked about on the
list.)

Upstream changes for proj (datumgrids 1.8 has no Changelog available):

PROJ 5.2.0

September 15th 2018
UPDATES

    Added support for deg, rad and grad in unitconvert (#1054)
    Assume +t_epoch as time input when not otherwise specified (#1065)
    Added inverse Lagrange projection (#1058)
    Added +multiplier option to vgridshift (#1072)
    Added Equal Earth projection (#1085)
    Added “require_grid” option to gie (#1088)
    Replace +transpose option of Helmert transform with +convention. From now on \ 
the convention used should be explicitly written. An error will be returned when \ 
using the +transpose option (#1091)
    Improved numerical precision of inverse spherical Mercator projection (#1105)
    cct will now forward text after coordinate input to output stream (#1111)