exchange: don't send stream data when server.uncompressed is set
Previously, bundle2 stream support would send out data even though
the streaming clone feature was disabled. This commit changes
the part handler to respect the server config.
Differential Revision: https://phab.mercurial-scm.org/D1930
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a