exception: prevent Cn::XH exceptions from spamming the logs
exception: prevent Cn::XH exceptions from spamming the logs

This is some sort of undocumented exception handling mechanism built on
top of C++ EH.

This needs testing.

relevant issues: #129 #139

thpatch/thcrap,thpatch/thcrap,thpatch/thcrap,thpatch/thcrap,thpatch/thcrap