Command-specific tab completion in kernel console

[Vojtech Horky]

Current mainline (rev. 1539) offers tab completion of kernel console commands and hints listing (see #50). The actual command is completed from list of commands. For arguments, symbol table is searched.

It would be more convenient to use this completion for call* commands only and provide context-specific completion for other commands. For example, test would offer list of existing tests while ipc could list existing tasks.

For the ipc or similar commands, the hint listing could be made more user-friendly by printing task name next to its number.

Printing the hints in more columns could be a next step.

Implementation note (idea): to avoid code repetition, command structure could be extended with two callback function - one for getting next hint and one for retrieving hits count for given prefix.

[Aurelio Colosimo]

A first implementation is in mainline, starting from rev. 2431 and improved in rev. 2438.
The callback mechanism is provided and hints may be given for any command, just by implementing the corresponding enumeration callback. At present, arguments hint is implemented for call* and test commands.