Fix warning due to yajl_status vs. yajl_gen_status

The yajl generator and parser use two different enums to list error codes.
This causes a compiler warning because a yajl_gen_status value is assigned to a
yajl_status type. The patch uses two separate variables to save the return
values of the generator and parser functions.
Use yajl_status_to_string
Merge branch 'master' of https://github.com/flightaware/yajl-tcl
Merge pull request #9 from gahr/master

Fix warning due to yajl_status vs. yajl_gen_status