[Click] Random changes

[Cliff Frey]

I have two other change that I'm debating pushing to mainline click.  The
backtrace debugging one I am definitely leaning towards porting, and I could
go either way on the bound-port-transfer change.  Any testing or feedback is
appreciated.

https://github.com/clifffrey/click/commit/cd08cd8b7a14310d029ab6911c701a6c1b1cdd0b
https://github.com/clifffrey/click/commit/6e5677a840ecd4991417335834c020ffd58099b0

commit 6e5677a840ecd4991417335834c020ffd58099b0
Author: Cliff Frey <cliff at meraki.com>
Date:   Tue Jan 4 21:51:42 2011

    Add easy-to-use userlevel backtrace debugging.

    If you run click with the CLICK_BACKTRACE=1 environment variable, it
    will dump a stack trace on many failures.


commit cd08cd8b7a14310d029ab6911c701a6c1b1cdd0b
Author: Cliff Frey <cliff at meraki.com>
Date:   Tue Jan 4 21:55:04 2011

    add --enable-bound-port-transfer config option

    This uses gcc extensions to remove one level of indirection from the
    virtual function calls done by push/pull.  I have not actually seen a
    measurable performance improvement from this (in my very limited
    testing).  I am curious if anyone else sees any performance win from
    it though.