added a simple compatibility spec for all fixtures
added a simple compatibility spec for all fixtures

this is based on Wasabi#inspect. the idea is to run as much of
the code for as many fixtures as possible to find problems without
having to write specs for every single feature.

introduces four spec failures.
savonrb/savon,SICSoftwareGmbH/savon,billr578/savon,Eric-Guo/savon,mpangrazzi/savon,oafridi/savon,enahum/savon,latortuga/savon,rtrepo/savon,zerobatu/savon