Fixed syscalls plug-in which was not operating do to a return in the init before defining callbacks. Added panda-args option for output log file. Added X86_64 target support.
Modifications to syscalls pull request. Closes #13

TARGET_I386 is also defined when x86_64 is built, so there's no need
to check for it twice. Also, the syscall instruction is valid in both
32-bit and 64-bit mode (it's the AMD version of sysenter), so we check
for both.
Merge branch 'master' of github.com:moyix/panda