GXemul Code2

Updating the OpenBSD/landisk guest operating system install instructions from 4.6 to 4.7.

HISTORY comment for r5734.

Adding a hack for outputting raw .ppm dumps of framebuffer contents. Useful for e.g. making movies of GXemul runs.

nbjoerg on #GXemul (FreeNode) noticed an easy way to trigger an unhandled case in memory_sh.cc. Hopefully this is the correct solution.

Use exit(0) instead of exit(1), per Andreas Ehliar's recommendation.

Remove callgrind and cachegrind output files on make clean, and adding a comment about using valgrind to the configure script.

Minor update of the guest OS documentation.

Updated TODO.

Bogus hack to machine_evbmips.cc to let RTEMS print some boot messages (again?) for mvme5500.

Adding configure script detection of -Wextra -Wno-unused-parameter -Wcast-align.