No need to set close_on_exec on read pipe
Improve encoding handling in parser for symbols
Marshal encoding for Symbols

This allows for storing and retrieving the encoding from the bytecode.
This is needed for supporting Symbols with encodings.
Add encoding support for Symbol

This is proably the simplest implementation based on what there is now.
In the future we want to rework the SymbolTable, but for now we can at
least support this.

Symbol encodings are used for example in the i18n gem, so there's real
code out there depending on this.
Remove tags for passing specs

Removes the tags for Symbol encoding related specs.