Accept flag parameter to optionally specify which pointers to free. This saves callers looping through the list to free pointers. ok + fix stsp@

Print the error message reported by the remote server when failing to update a branch (for e.g. because of a server-side check.) Reported by gonzalo@, with help and ok stsp@.

Needed by future gotd(8), where progress reports will be sent to a network socket, rather than a local terminal.

Future gotd(8) needs to run got_pack_create() in a chroot environment, so we can no longer open new temporary files inside got_pack_create(). ok op@

The old code required a seekable output file. This conflicts with requirements of future gotd(8), which will write pack file data to network sockets. ok op@

With the narrow scope of bytes_sent_cur it would always be zero, and we would always update progress. Found by llvm's scan-build (Dead store). OK stsp

ok op@

Problem reported and fix tested by Omar Polo.

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.

Let realloc_ids() take as argument the number of entries to allocate. Do not allocate an extra chunk. ok stsp

realloc_ids() is called again in the loops that assign to the ID arrays, before the first assignment. ok stsp

The git protocol spec says the client MUST NOT send a pack file if the only command used is 'delete'. Fixes 'got send -d' against Github's server which closed the session upon receiving the empty pack file we sent. This problem wasn't caught by regression tests since git-daemon does accept an empty pack file. Problem reported by jrick.