getSortStringForRow() passed a parameter as hdr, but referred to it as msgHdr

This throws an error normally, and seems to be at least partially responsible
for the conversation window getting wedged and never displaying a new message
in some cases.
message.js: trying to set character set throws exception, prevents msg display

Trying to force the character set to UTF-8 here throws a
NS_ERROR_XPC_CANT_MODIFY_PROP_ON_WN exception and prevents
the conversation window displaying at all in Thunderbird 31.0.

Commenting out these 3 lines fixes the problem.
Merge branch 'WrappedObject-fix'