REL-1811: Additional P2 warnings if p-offsets are used with slit spectroscopy.
Comparisons of double values now use a delta value.
REL-1811: Fixed a compile bug after improper merging.
REL-1811: After last change getFPU does not return null anymore, don't need to check for that.
REL-1811: Final code cleanup, minimal tests.
REL-1811: Consolidated similar code in a new rule that can be used by different instruments.
Merge pull request #15 from fnussber/feature/REL-1811

REL-1811: Slit spectroscopy phase-2 check for P-offsets
REL-1436: Fix compareTo method of Alloc objects.