More JTAG interface driver cleanup:

- Make interface_jtag_execute_queue call new helper function.
- Add default_interface_jtag_execute_queue to wrap jtag interface access.

This patch may look useless on its own, but it helps to isolate the core
JTAG variables from the interface_jtag_* routines, so the later can be
moved into jtag_driver.c in a pending patch.


git-svn-id: svn://svn.berlios.de/openocd/trunk@1993 b42882b7-edfa-0310-969c-e2dbd0fdcd60