PHP directors - generate call_user_function on one line
Fix %naturalvar and templated methods using enums

%naturalvar was not being picked up - use the symbol table instead for
looking up the feature.

use_naturalvar_mode() has been moved to Language class (not strictly necessary though)
Remove incorrectly and newly introduced assert

Was failing in li_boost_shared_ptr.i for some languages. A similar
testcase has been added into naturalvar_more.i.