Added support for partial wildfire headers

Partial wildfire headers are described at http://www.firephp.org/Wiki/Reference/Protocol
as having the following structure:

    X-Wf-1-1-1-1	17245|[{"Type":"LOG"},["Element 0","Element 1", ... |\
    X-Wf-1-1-1-2	| ... ,"Element 399", ... |\
    X-Wf-1-1-1-3	| ... ,"Element 799"]]|
s/Exception/Error/
Merge pull request #16 from weirdan/master

Support for partial headers