Handle linker scripts

[wadey]

On some OSes (such as Ubuntu linux), a .so file can contain a linker script which will point to the correct shared library to use. This will cause dlopen to raise an error.

As an example, here is what /usr/lib/libc.so looks like on Ubuntu 10.04:

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /lib/libc.so.6 /usr/lib/libc_nonshared.a  AS_NEEDED ( /lib/ld-linux-x86-64.so.2 ) )

I found this Haskell GHC ticket from when they ran into the same problem: http://hackage.haskell.org/trac/ghc/ticket/2615 . I ported their solution to node-ffi (basically, see if the error message is "invalid ELF header" and then try to read the file and look for the GROUP section).