* Create mark/sweep functions for transports.
* Create a transport_resolve_conflicts() function that tries to
  resolve conflicts when registering transports.

* Use strcmpstart() instead of strcmp(x,y,strlen(y)).
* Warn the user if the managed proxy failed to launch.
* Improve function documentation.
* Use smartlist_len() instead of n_unconfigured_proxies.
* Split managed_proxy_destroy() to managed_proxy_destroy()
  and managed_proxy_destroy_with_transports().
* Constification.

If multiple torrc transport lines have the same argv, tor instructs a
single managed proxy to launch multiple protocols.

* Restored "proxy" in external ServerTransportPlugin lines.
* Changed the extended OR port and ORPort env. vars to addr:port.

* Add some utility transport functions in circuitbuild.[ch] so that we
  can use them from pt.c.
* Make the accounting system consider traffic coming from proxies.
* Make sure that we only fetch bridge descriptors when all the
  transports are configured.

* Create a function that will get input from a stream, so that we can
  communicate with the managed proxy.
* Hackish change to tor_spawn_background() so that we can specify an
  environ for our spawn.

Returning a tristate is needless here; we can just use the yielded
transport/proxy_type field to tell whether there's a proxy, and have
the return indicate success/failure.

Also, store the proxy_type in the or_connection_t rather than letting
it get out of sync if a configuration reload happens between launching
the or_connection and deciding what to say with it.

    - const-ify some transport_t pointers
    - Remove a vestigial argument to parse_bridge_line
    - Make it compile without warnings on my laptop with
      --enable-gcc-warnings

Multiple Bridge lines can point to the same one ClientTransportPlugin
line, and we can have multiple ClientTransportPlugin lines in our
configuration file that don't match with a bridge. We also issue a
warning when we have a Bridge line with a pluggable transport but we
can't match it to a ClientTransportPlugin line.

* Tweaked doxygen comments.
* Changed returns of get_proxy_addrport().
* Ran make check-spaces.
* Various small code tweaks.

* Renamed transport_info_t to transport_t.
* Introduced transport_get_by_name().
* Killed match_bridges_with_transports().
  We currently *don't* detect whether any bridges miss their transports,
  of if any transports miss their bridges.
* Various code and aesthetic tweaks and English language changes.

It creates some helper functions that return the proxy type, proxy addr/port, etc.

Not included in the previous commit, because the implementation is
ugly; I see no other way of doing this though.

* Improved function documentation.
* Renamed find_bridge_transport_by_addrport() to
  find_transport_by_bridge_addrport().
* Sanitized log severities we use.
* Ran check-spaces.