Fix DoS vulnerability in restrict_access

Symbols are not garbage collected, so if .to_sym is called on (a subset of) params, visitors/users can create unlimited symbols, effectively doing a DoS attack against the server.

This commit fixes the DoS vulnerability by making the restrict_access method check against strings instead of symbols.
Implemented 'fulltext match' or 'sphinx match' to use fulltext search in node query. Fix #74.
Merge branch 'master' of github.com:zena/zena