tests: load showstack in test-pull-http.t so network hangs are easier to find

This also gives us some minimal "it loads" coverage on showstack,
which I rather like. showstack doesn't work on Windows per mbarbison,
so it's disabled there.

I added this in service of debugging a hang introduced on Python 3 by
revision a88d68dc3ee8. I'm still not sure what the problem there is,
but this at least gives us a little bit of a chance to figure out
what's going on.

Differential Revision: https://phab.mercurial-scm.org/D3247

tests/test-pull-http.t

@@ -1,79 +1,90
 #require killdaemons
 
+#if no-windows
+For debugging: this is a pretty simple test that is a good candidate
+for tracking down network-related bugs. Sometimes a command in this
+hangs, so having showstack pre-loaded is sometimes helpful. This also
+gives us a test that at least proves showstack can be loaded.
+  $ cat >> $HGRCPATH <<EOF
+  > [extensions]
+  > showstack = $TESTDIR/../contrib/showstack.py
+  > EOF
+#endif
+
   $ hg init test
   $ cd test
   $ echo a > a
   $ hg ci -Ama
   adding a
   $ cd ..
   $ hg clone test test2
   updating to branch default
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ cd test2
   $ echo a >> a
   $ hg ci -mb
 
 Cloning with a password in the URL should not save the password in .hg/hgrc:
 
   $ hg serve -p $HGPORT -d --pid-file=hg.pid -E errors.log
   $ cat hg.pid >> $DAEMON_PIDS
   $ hg clone http://foo:xyzzy@localhost:$HGPORT/ test3
   requesting all changes
   adding changesets
   adding manifests
   adding file changes
   added 2 changesets with 2 changes to 1 files
   new changesets cb9a9f314b8b:ba677d0156c1
   updating to branch default
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ cat test3/.hg/hgrc
   # example repository config (see 'hg help config' for more info)
   [paths]
   default = http://foo@localhost:$HGPORT/
   
   # path aliases to other clones of this repo in URLs or filesystem paths
   # (see 'hg help config.paths' for more info)
   #
   # default:pushurl = ssh://[e-mail]/hg/jdoes-fork
   # my-fork         = ssh://[e-mail]/hg/jdoes-fork
   # my-clone        = /home/jdoe/jdoes-clone
   
   [ui]
   # name and email (local to this repository, optional), e.g.
   # username = Jane Doe <[e-mail]>
   $ killdaemons.py
 
 expect error, cloning not allowed
 
   $ echo '[web]' > .hg/hgrc
   $ echo 'allowpull = false' >> .hg/hgrc
   $ hg serve -p $HGPORT -d --pid-file=hg.pid -E errors.log
   $ cat hg.pid >> $DAEMON_PIDS
   $ hg clone http://localhost:$HGPORT/ test4 # bundle2+
   abort: authorization failed
   [255]
   $ hg clone http://localhost:$HGPORT/ test4 --config devel.legacy.exchange=bundle1
   abort: authorization failed
   [255]
   $ killdaemons.py
 
 serve errors
 
   $ cat errors.log
   $ req() {
   >     hg serve -p $HGPORT -d --pid-file=hg.pid -E errors.log
   >     cat hg.pid >> $DAEMON_PIDS
   >     hg --cwd ../test pull http://localhost:$HGPORT/
   >     killdaemons.py hg.pid
   >     echo % serve errors
   >     cat errors.log
   > }
 
 expect error, pulling not allowed
 
   $ req
   pulling from http://localhost:$HGPORT/
   abort: authorization failed
   % serve errors
 
   $ cd ..