ch2: fix Makefile and add a 'run' rule.

We need to explicitly specify the x86-32 flag to compiler because
the assembly code is 32-bit and the compiler might be 64-bit.

'make run' is very convenient for testing.
ch2: fix domain_config, using full path for kernel

Not sure why it requires full path.
ch2: fix guest type to support PAE.

Xen 4 does not support xen-3.0-x86_32 guest any more, and it requires the
guest supports PAE if the guest is 32-bit.
.gitignore: add more rules into .gitignore