Changes done for the Interval Arithmetic package.

Version 2.1 on 11 September 1998
- "lines too long" problem fixed.
- removed temporary objects => faster.

Version 2.0 on 17 August 1998.
- Added CGAL_to_interval_nt() cast functions for Gmpz and
  leda_{real,rational,integer,bigfloat}.
- Added operators +=, -=, *=, /=, as required for all CGAL NTs.
- Moved private files to the directory CGAL/Interval_arithmetic
- Doc update: cgal.bib removed, geombib is updated.
- Using CVS.
- [sent Stefan the necessary updates to other NTs].

Version 1.6 on 10 May 1998.
- "package" line added in the headers.
- Added a CGAL_warning_msg() when you compare 2 overlapping intervals,
  disabled by the compilation flag CGAL_IA_NO_WARNINGS (or CGAL_NO_WARNINGS).
- New private member function: overlap() (same semantic as operator==()).
- Doc updates:
  - better introduction.
  - fixed bugs shown by the HTML version.
  - update the support status for the Alpha.
  - modifications from Remco for 1.0.
  - reference to our (BBP) ACM SoCG'98 paper added.
- ChangeLog file created.


Version 1.5 on 26 February 1998.
- Added "#include <assert.h>" forgotten in 1.4.


Version 1.4 on 6 February 1998.
- Changed _FPU_* to CGAL_FPU_*.
- Doc updates.


Version 1.3 on 16 December 1997.
- Added an assertion when defining an interval with the lower bound greater
  than the upper.  Disabled when CGAL_NO_PRECONDITIONS is defined.


Version 1.2 on 16 December 1997.
- Added support for old Irix 5.3 include files.


Version 1.1 on 16 December 1997.
- lines too long problem fixed.


Version 1.0 on 3 December 1997.
- initial version based on some C code, and 2 C++ wrapper classes for CGAL.