tests/test-bad-extension.t

tests: add script to disable a selected wire protocol capability

This can be used to test that the client and server both fall back to the
previous wire protocol when the capability is not supported.

It is currently used by test-push-http.t and I plan to use it for the HTTP
long argument support tests.

  $ echo 'raise Exception("bit bucket overflow")' > badext.py
  $ abspath=`pwd`/badext.py

  $ echo '[extensions]' >> $HGRCPATH
  $ echo "gpg =" >> $HGRCPATH
  $ echo "hgext.gpg =" >> $HGRCPATH
  $ echo "badext = $abspath" >> $HGRCPATH
  $ echo "badext2 =" >> $HGRCPATH

  $ hg -q help help
  *** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
  *** failed to import extension badext2: No module named badext2
  hg help [TOPIC]
  
  show help for a given topic or a help overview