New codes: FUND_MAX_EXCEEDED, FUND_CANNOT_AFFORD, FUND_DUST_LIMIT_UNMET.
The error message "Cannot afford fee" was not exactly correct because
it would also occur if the amount requested could not be afforded. So
I changed it to the more generic "Cannot afford transaction".
Other things:
* Fixed off-by-one satoshi in fundchannel manpage.
* Changed 'arror' to 'error' because we are not pirates.