tests/test-mq-qsave.t

lfs: default the User-Agent header for blob transfers to 'git-lfs'

The custom User-Agent for blob transfers was added in e7bb5fc4570c.  Now I've
hit another incompatibility with a server wanting the string to start with
'git' or 'git-lfs' [1].  I don't feel strongly about this either way, but a
Wireshark trace of git shows that when the Batch API is hit, the User-Agent is
'git-lfs/2.3.4'.  So this would probably ensure maximum interoperability.

This still leaves the experimental knob in, just in case.

[1] https://bitbucket.org/sdorra/scm-manager/src/095a027178888bc2b819aebfae3d2c192c858030/scm-plugins/scm-git-plugin/src/main/java/sonia/scm/web/GitUserAgentProvider.java?at=default&fileviewer=file-view-default#GitUserAgentProvider.java-117

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "mq=" >> $HGRCPATH

  $ hg init

  $ echo 'base' > base
  $ hg ci -Ambase
  adding base

  $ hg qnew -mmqbase mqbase

  $ hg qsave
  $ hg qrestore 2
  restoring status: hg patches saved state