MI fine-grained versioning

[Vladimir Prus]

At the moment, MI does not have any mechanism to announce supported
features. For example, I have a patch to add "frozen" variable objects. To support
such feature in a backward-compatible fashion, the frontend must know if that
features is supported by the given gdb binary.

Using version number is not very reliable -- for example if you use the CVS state
of gdb, the version number is not yet bumped.

Yet another approach is to "detect" presence of feature by trying some commands,
or by trying commands with some new options, or by constructing more contrived test
cases. However that's troublesome.

How about adding new MI command that returnes list of supported fine-grained features.
For example:

	-list-features
	^done,result=["frozen_variables","info_path_expression"]

The MI manual would contain a section listing all feature names and briefly documenting them.

Comments?

- Volodya