[Proj] Small errors in modified stereographic

[Oscar van Vlijmen]

Recently I checked the code from the files:
  PROJ 4.6.0: PJ_mod_ster.c
  libproj4v3: proj_mod_ster.c,v
There is a small error in the value of coefficient 'A3' in the projection
lee_os, and the wrong value of phi0 in the projection gs48.
The values according to Snyder are:
  A3_Lee = -0.00881625 (not -0.0088162)
  phi0_GS48 = 39.0 (not -39.0)
cf. J. P. Snyder: Map projections, a working manual, PP 1395, Ch. 26, p. 209
I assume the Snyder values are correct.

No big deal for lee_os, but gs48 will probably give completely wrong
results.
Who cares? Nobody ever uses these projections.
For those who do care: you might want to correct your code.