[cs] optimize fields interation in generic casting (same as 5641834de3ad00ad5c228fe2dfd844a85c9f4c6d)
minor [skip ci]
[cs] Added Lib.rethrow
add recent cs/java changes to CHANGES.txt
[python] clean up python.Boot a bit
[python] use Math.round instead of own function
[python] minor Reflect cleanup