push: do not let configured foreign-vcs permanently clobbered

push: do not let configured foreign-vcs permanently clobbered

Recently, 6f48d39 (clone: delay cloning until after remote HEAD checking,
2012-01-16) tried to record if a remote helper needs to be called after
parsing the remote when transport_get() is called, by overwriting the
field meant to store the configured remote helper name in the remote
structure.

This is OK when a remote represents a single remote repository, but fails
miserably when pushing to locations with multiple URLs, like this:

    $ cat .git/config
    [remote "origin"]
        url = https://code.google.com/p/git-htmldocs/
        url = github.com:gitster/git-htmldocs.git
        push = refs/heads/master:refs/heads/master
    $ git push

The second url that is supposed to use the git-over-ssh transport
mistakenly use https:// and fails with:

    error: Couldn't resolve host 'github.com:gitster' while accessing
    github.com:gitster/git-htmldocs.git/info/refs
    fatal: HTTP request failed

The right solution would probably be to dedicate a separate field to store
the detected external helper to be used, which is valid only during a
single use of transport until it is disconnected, instead of overwriting
foreign_vcs field, but in the meantime, this band-aid should suffice.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>