Fix bugs from last night

[adamchalmers]

Wrote two bugs last night:

1. The HTTP spec says that if the client sends Expect: 100-continue, the server should send a preliminary status HTTP/1.1 100 Continue response back, then wait for the client to send the body, then the server sends the real HTTP status (e.g. 200 OK) with headers + body. Our implementation didn't send the real HTTP status back, it skipped straight to sending the response headers + body.
2. Used max instead of min when trying to limit how many bytes the server would write at once.

Also, I investigated OS Error 22 more. I used strace to figure out which system call was causing an error (it was write) then looked up its manpage with man 2 write. It says it can only handle INT_MAX bytes in a single write, and it won't do a partial write if you write more than that, it'll just fail. On my platform, INT_MAX is (2^31) so we limit to that.