ice2slice: bug with return value and more

[bernardnormier]

There are several issues with ice2slice. A good test is to convert https://github.com/mumble-voip/mumble/blob/master/src/murmur/MumbleServer.ice

1. A single return type is not converted properly, e.g.

idempotent nameToId(name: string) -> returnValue: int32

(the returnValue: is incorrect)

2. proxy parameters are not mapped correct, e.g.

addCallback(cb: MetaCallback) throws (InvalidCallbackException, InvalidSecretException)

Should be MetaCallbackProxy?.

3. Docs comments on sequence (and presumably dictionary) are lost.

4. It would be nice to generate additional comments in the output file:

• the file was generated by ice2slice from Xxx.ice
• some metadata in the source file (like python:seq:tuple) could not be converted
• const int PermissionWhisper = 0x100; and associated doc-comments were not converted