Remove un-const-ing from method invocation funcs.
Remove un-const-ing from method invocation funcs.

Method invocation functions have been casting away const-ness by
accepting `const prefix_Foo *self` as the invocant but then invoking
the retrieved function pointer with `self` cast to `(prefix_Foo*)`.
This was necessary to avoid warnings from "const CharBuf" immutable
strings -- but now our String type is immutable without requiring
`const`, allowing us to improve type safety by removing the cast.

kidaa/lucy,rbevers/lucy,nwellnhof/lucy,rectang/lucy,rbevers/lucy,pombredanne/apache-lucy,rectang/lucy,nwellnhof/lucy,kidaa/lucy,nwellnhof/lucy,rbevers/lucy,apache/lucy,pombredanne/apache-lucy,rectang/lucy,rectang/lucy,apache/lucy,pombredanne/apache-lucy,nwellnhof/lucy,kidaa/lucy,kidaa/lucy,kidaa/lucy,rectang/lucy,nwellnhof/lucy,apache/lucy,nwellnhof/lucy,rbevers/lucy,kidaa/lucy,rbevers/lucy,rbevers/lucy,apache/lucy,kidaa/lucy,kidaa/lucy,apache/lucy,pombredanne/apache-lucy,pombredanne/apache-lucy,apache/lucy,rbevers/lucy,pombredanne/apache-lucy,rectang/lucy,apache/lucy,rectang/lucy,pombredanne/apache-lucy,nwellnhof/lucy