Checking for ET_EXEC

[Rayiner Hashem]

In ../stage2/i386-elf.h in GRUB 0.90, you define a macro that checks if an ELF 
file is bootable. In it you check to see if the filetype is equal to ET_EXEC. 
This isn't necessarily the best thing to do. It is sometimes appropriate to 
build a kernel as a shared library (.so, of type ET_DYN) as it makes kernel 
modules behave very similar to regular userspace modules. You might want to 
consider removing the test for ET_EXEC.