Fixes #2482

And also add proj_context_errno_string()

Revise gie 'expect failure errno XXXX' strings

In that mode:
* All non-comment/decoration lines must start with a valid tag
* Commands split on several lines should be terminated with " \"

This commit adds five new projections to PROJ:

    adams_hemi: Adams Hemisphere in a Square
    adams_wsI:  Adams World in a Square I
    adams_wsII: Adams World in a Square II
    guyou:      Guyou
    peirce_q:   Pierce Quincuncial

The code originates from Gerry Evendens libproject and has been adapted
to work with modern PROJ. To ensure that the modified code works as
intended extensive test data has been created using libproject and
sproj so that no errors occured when porting from libproject to PROJ.
The test data is wrapped in a gie files. All test cases reproduce
results from libproject at the mm level.