my_seek() and my_tell() functions now honour MY_WME flag.


include/mysys_err.h:
  Fix for bug#48451: my_seek and my_tell ignore MY_WME flag
    - EE_CANT_SEEK added, used in my_seek() and my_tell() functions.
mysys/errors.c:
  Fix for bug#48451: my_seek and my_tell ignore MY_WME flag
    - EE_CANT_SEEK added, used in my_seek() and my_tell() functions.
mysys/my_seek.c:
  Fix for bug#48451: my_seek and my_tell ignore MY_WME flag
    - my_seek() and my_tell() handle MY_WME flag.
mysys/my_symlink.c:
  Fix for bug#48451: my_seek and my_tell ignore MY_WME flag
    - __attribute__((unused)) removed, as myf MyFlags is
  actually used in the my_realpath() function.
storage/myisam/ha_myisam.cc:
  Fix for bug#48451: my_seek and my_tell ignore MY_WME flag
    - check my_seek() result.