bug 1661: rebuild_zebra.pl changes

bug 1661: rebuild_zebra.pl changes

[1] Use File::Temp to create and manage
    export directory if -d is not specified.
[2] Added usage message.
[3] Code that attempts to fix up Zebra
    configuration files changed so that it
    is invoked only if --munge-config option
    is supplied; this code will ultimately
    either be removed or moved to a separate
    script -- the sorts of errors that it
    tries to fix should no longer be appearing
    in a standard install.
[4] Fixed Win32 portability problem when removing
    temporary directory.

Signed-off-by: Chris Cormack <crc@liblime.com>
Signed-off-by: Joshua Ferraro <jmf@liblime.com>