relax SVN archive

Another raise() function call to statement change for 2to3 preparations.

Converted some raise() function calls to raise statements in preparation for the 2to3 conversion.

Converted the ScientificPython PDB reader to support both Python 2 and 3.

The command used was:
2to3 extern/scientific_python/IO/PDB.py -w

The __repr__() method was manually modified due to the 'list' variable clashing with the 'list'
type.

Created a new module for simultaneous Python 2 and 3 support in relax called 'compat'.

Python 3 fixes - the list() function is now used in combination with range() to generate the ordered list.

range() in Python 3 is an iterator object (just as xrange was), so now the list() function has to be
called.

Python 3 preparations - mass conversion of all xrange() calls to range().

Fix for a bug introduced at r17624 in the generic_fns.sequence.validate_sequence() function.

The is_none() function call doesn't seem to be working correctly.

Created the special check_types.is_filetype() function for checking for files in all Python versions.

Python 3 - Eliminated an unneeded xrange call.

Python 3 - eliminated the use of the map() function, as this behaves differently in Python 3.