S2EExecutor: function to enable instruction printing from gdb

Useful for debugging, setting the llvm option from GDB does not
seem to work.

Signed-off-by: Vitaly Chipounov <vitaly.chipounov@epfl.ch>
Expose internal KLEE headers to S2E

Signed-off-by: Vitaly Chipounov <vitaly.chipounov@epfl.ch>
Reworked device state snapshotting

Features:
 - Use KLEE address space to store disk state
 - Centralize all snapshotting in one place in S2EExecutor

Signed-off-by: Vitaly Chipounov <vitaly.chipounov@epfl.ch>
build: Remove stray command from clean target

Signed-off-by: Diego Biurrun <diego@biurrun.de>