posix: implement readpipe using non-blocking I/O (issue4336) On Linux, fstat().st_size of a pipe always returns 0, even if the pipe has data available for reading. This meant that reading from and subsequently printing the stderr pipe content after wireproto commands over SSH meant that available data wasn't being printed. We now implement pipe reading on POSIX by doing a non-blocking read for all available data.

platform: implement readpipe() Reading all available data from a pipe has a platform-dependent implementation. This patch establishes platform.readpipe() by copying the inline implementation in sshpeer.readerr(). The implementations for POSIX and Windows are currently identical. The POSIX implementation will be changed in a subsequent patch.

exchange: remove duplicated addition to pushop.stepdone Not sure how it got there but it is useless.

exchange: drop superfluous parens

push: add bookmarks to the unified bundle2 push We use the `pushkey` part to exchange bookmark updates within the unified bundle2 push. Note that this only applies on update (moving a bookmark known on both sides) since bookmark export (creation of a new bookmark on remote) is apparently done outside of the _push function.

test-bundle2: add bookmark movement to the push test If we add bookmarks to bundle2, we need a way to test the new code. Tests are changed beforehand to highlight that inclusion of bookmarks in bundle does not introduce any behavior changes.

push: use stepsdone to control bookmark push If bookmark are to be integrated in the unified bundle2, we need a way to disable the old-style push.

push: move bookmark discovery with other discovery steps The discovery of necessary bookmark updates is now done within the "discovery phase". This opens the door to the inclusion of bookmarks in a unified bundle2 push.

pushbookmark: split an ultra-long line into a saner version We make a temporary variable for the remote bookmark data and we do not expand all elements from `bookmark.compare` since we are going to use only one.

revert: drop dead code for untracked files Untracked files are handled through status now.