Currently the "debug_level 3" command tracing ignores commands
that could return values to TCL scripts (by plugging in to a
slightly lower level of the interpreter stack).

Fix that by abstracting the tracing command and starting to
make some of those previously-untraced commands use this new
mechanism.


git-svn-id: svn://svn.berlios.de/openocd/trunk@2224 b42882b7-edfa-0310-969c-e2dbd0fdcd60