- Improves error handling upon GDB connect

- switch to synchronous halt during connect. This fixes the bug
  where poll() was not invoked between halt() and servicing the
  'g' register packet
- halt() no longer returns error code when target is already halted, just
  logs a warning. Only the halt() implementation can say anything
  meaningful about why a halt() failed, so error messages are pushed
  up to halt()
- fixed soft_reset_halt infinite loop bug in arm7_9_common.c. The rest
  of the implementations are still busted.
- by using USER() instead of command_print() the log gets the 
  source + line #. Nice.
- no longer invoke exit() if soft_reset_halt fails. A reset can often 
  fix the problem.

git-svn-id: svn://svn.berlios.de/openocd/trunk@475 b42882b7-edfa-0310-969c-e2dbd0fdcd60

src/target/target.h

@@ -116,7 +116,7 @@ typedef struct target_type_s
 	/* target request support */
 	int (*target_request_data)(struct target_s *target, u32 size, u8 *buffer);
 
-	/* target execution control */
+	/* halt will log a warning, but return ERROR_OK if the target is already halted. */
 	int (*halt)(struct target_s *target);
 	int (*resume)(struct target_s *target, int current, u32 address, int handle_breakpoints, int debug_execution);
 	int (*step)(struct target_s *target, int current, u32 address, int handle_breakpoints);
@@ -270,7 +270,6 @@ int target_arch_state(struct target_s *target);
 #define ERROR_TARGET_INVALID	(-300)
 #define ERROR_TARGET_INIT_FAILED (-301)
 #define ERROR_TARGET_TIMEOUT	(-302)
-#define ERROR_TARGET_ALREADY_HALTED (-303)
 #define ERROR_TARGET_NOT_HALTED (-304)
 #define ERROR_TARGET_FAILURE	(-305)
 #define ERROR_TARGET_UNALIGNED_ACCESS	(-306)