httpsendfile: record progress information during read()
This allows us to provide deterministic progress information during
transfer of bundle data over HTTP. This is required because we
currently buffer the bundle data to local disk prior to transfer since
wsgiref lacks chunked transfer-coding support.
localrepo: remove unneeded os.unlink call in wwrite
The opener already unlinks the filename before 'w'riting, for both
the symlink and the normal file case. It also now resets the flags
for normal files on 'w'rite, which makes this os.unlink call completely
redundant.
For Windows, removing this extra unlink call helps to avoid tripping
issue2524 (os.unlink followed by a write).
opener: always reset flags on 'w'rite
only the patcher needs to preserve flags on write