avoid changing the data header

strtok adds \0's to the input string, this can cause problems if the
request is later proxied to some remote server
small optimization
G2O signs the query string as well

by default G2O signs the whole URI including the query string, need to use
r->unparsed_uri, instead of r->uri which contains only the URI path
Merge pull request #6 from erankor/master

avoid changing the data header while parsing it