relax SVN archive

Bug fix for the BMRB system test initialisation for when the bmrblib module is missing.

The base __init__() method needs to be initialised first.

Python 3 preparations - the unit tests are now fully Python 2 and 3 compatible.

The command used was:
2to3 -w -f except -f import -f imports -f long -f numliterals -f xrange .

Python 3 preparation - all of the _generic_fns unit tests now use absolute module imports.

Python 3 preparations - all the _prompt unit tests now use absolute module imports.

Python 3 preparation - removed all xrange() calls from the unit tests, these are not needed.

Last Python 3 compatibility update for the system tests - they are now both Python 2 and 3 compatible!

The command used was:
2to3 -w \
-f except \
-f import \
-f imports \
-f long \
-f numliterals \
-f xrange \
.

Python 3 preparation - the test_suite.system_tests package now uses the absolute module path for imports.

Python 3 preparation - changed the import of SystemTestCase to use the absolute module path.

Removed all of the xrange() calls from the system tests as these are not necessary.

This is in preparation for Python 3.

Fix for a fatal bug introduced in the last revision (r17576).