Fix includes for test target in xcode file
IAU rotation model uses days since J2000

Fixes issue where the rotation model would use days since the start of the
Julian period instead of since the start of the J2000 epoch.
Fix test so that it use the new obliquity constants
Compute simple derivative of w in iau rotation model

Also undoes the invalid assumption in 81936ed4236c73abbbcdee416029e221d2e2ba07
Fix radian count for rotation quaternion generation

90 degrees is pi/2 not pi/4 (ooups)