FuzzyHash: if disable giving an run time error instead of config

FuzzyHash operator is optional and only installed if the headers for libfuzzy
was found in the system. Otherwise, the FuzzyHash operator is disable during
the compilation. After this commit, if some rules tries to use it, ModSecurity
will produce an runtime error not a config time error, allowing the web server
to procede normal with its operations.
Declares msre_var *rvar at the beggining of the function

Necessary to fix the build on Win8 VS 2011