Ensure that \ is not allowed in filenames, even on Unix


include/my_dbug.h:
  Rename: include/dbug.h -> include/my_dbug.h
include/Makefile.am:
  Change dbug.h -> my_dbug.h
include/my_global.h:
  Change dbug.h -> my_dbug.h
libmysql/get_password.c:
  Change dbug.h -> my_dbug.h
libmysqld/lib_vio.c:
  Change dbug.h -> my_dbug.h
sql/table.cc:
  Ensure that \ is not allowed in filenames, even on Unix