- ignore data aborts during gdb memory read packets by default, and return 0x0 instead

- add configuration option "gdb_report_data_abort <enable|disable> to enable reporting of data aborts during gdb memory read packets
- thanks to Øyvind Harboe for identifying the problem with GDB and data aborts
- fix some warnings in gdb_server.c



git-svn-id: svn://svn.berlios.de/openocd/trunk@307 b42882b7-edfa-0310-969c-e2dbd0fdcd60