Commit Briefs
make tmp dir location a compile-time setting and change gotweb's tmp dir
We are not sure whether a gotweb package can own /var/www/tmp on OpenBSD. Moving gotweb's tmp dir to /var/www/got/tmp sidesteps that issue.
got_error_from_errno -> got_error_prefix_errno
also add got_error_prefix_errno2 and got_error_prefix_errno3 which should hopefully all be merged into a single function with variadic args (but can't alloc mem)