fast Shuffle product compatible with iterable objects (use linear extension)

ticket 15595

fast Shuffle product (use linear extension) compatible with iterable objects.

ticket 15595

append licence GPL

delete a wrong test
Merge branch 'shuffle/15595' into shufflee/15595
trac 15595: Shuffle more efficient + some documentation + doctest
add ome documentation
framework for double description method implementation
initial implementation of double description algorithm
add missing '_'s
fix the FIXME comment
Shuffle product documentation and idioms in Python.
finished double description implementation
finished Hrep2Vrep
Vrep2Hrep for the case of no lines
start generic polyhedra backend
towards full docstring coverage
full doctest coverage
add to geometry reference manual
clean up docs
Merged 6.3.beta1
Trivial changes to double description patch.
rename DEBUG -> VERIFY_RESULT