added more benchmarks
S4 support, warnings for non-supported, tests

S4 support now implemented through , non supported types
will throw warnings
fix inherits, special attrs

Got rid of the environment argument for evaluating the inherits
call in and now just evaluate in base environment.  Attributes of
types EXTPTRSXP, WEAKREFSXP, BCODESXP, ENVSXP don't need to be identical
when evaluating in special attrs mode
new special attrs only special with attr_mode==0
testing inherits can't be hijacked
added some data.table tests