Correctives in some CDL files for package gp

In the files gp_Pnt.cdl and gp_XYZ.cdl, some comments (for classes and methods)
either do not correspond with reality (e.g. "method Z() returns X coordinate of
the point") or contain obsolete terms (e.g. "non-persistent") or incorrect
terms (e.g. "a number triple"). These defects have been corrected. Incorrect
terms have been replaced with more correct ones (e.g. "a XYZ object" instead
of "a number triple").