Fixes for rustc 0.13.0-nightly (c46812f65 2014-10-19 00:47:18 +0000)
Rust no longer has find_or_insert_with op
Remote unused attribute
Fix outdated TODO
Regenerate files with protoc 2.5.0
Default values for fields

Enum default values are not yet implemented
Properly escape default values of string type
Code cleanup
Scope abstraction

This should make codegen and reflection code easier to maintain.
Move descriptor data to the bottom of generated file

It makes generated files look a little nicer.
name is required operation for FieldAccessor
fail -> panic
Configurable opt-level with RUST_PROTOBUF_OPT env var

Also include -g flag by default
More default values

* implement default values for enums
* fix default values in mut_ operations
mut_ operations are not needed for pritmitive types
Use unwrap_or(...) for primitive types

... instead of unwrap_or_else(|| ...). It makes generated code slightly
easier to read by humand and by compiler.
Add comments about fields to generated file
Only generate for files, listed in file_to_generate

... as required in plugin.proto comments.
Default values are implemented now
Allow more identifiers in .proto files