imsg_clear frees and closes resources allocated as part of enqueueing imsgs so it's a no-op after reads. discussed with and ok stsp@

Problem reported by naddy. ok naddy

Always announce all local references to the server when fetching changes. We used to do this only in mirror mode. In regular mode only refs/tags and refs/remotes/origin were announced, which could result in unnecessary downloads if relevant objects exist in refs/heads or elsewhere.

This function is now being used by both 'got fetch' and 'got send' so its former name was misleading.

Both GOT_FETCH_PKTMAX and GOT_SEND_PKTMAX had the same value. Declare this value as GOT_PKT_MAX in got_lib_pkt.h instead.

These functions are used by 'got send' and 'got fetch' in order to open network connections to a server. Move them into new file lib/dial.c and declare relevant functions in got_dial.h and lib/got_lib_dial.h. No functional change.

On Linux, pipes returned from pipe(2) only work in one direction. This broke 'got clone' over ssh in the -portable version because got-fetch-pack assumes it can use its fetchfd for both reading and writing. I wrote a complicated diff to use two pipe(2) calls instead of one, but millert suggested a simpler solution: Use socketpair(2) instead of pipe(2). ok millert jrick tracey

Simplify dial_git() by formatting the initial Git protocol packet with dprintf, suggested by millert, and stop leaking an asprintf buffer. ok stsp

ok millert, naddy