Fix an invalid pointer dereference in a test.
Change funptr's [release_runtime_lock] argument to [runtime_lock].

The [funptr] view can be used in either direction.  When [funptr] is
used to call C from OCaml, [runtime_lock] determines whether the lock
is released.  When [funptr] is used to call OCaml from C,
[runtime_lock] determines whether the lock is acquired.
Optionally acquire the runtime lock in the callback handler.
A test for the [runtime_lock] argument to [funptr].
Merge pull request #171 from yallop/funptr-acquire-lock

Support for acquiring the runtime lock in callbacks
Move the cptr type from Static to Ctypes_raw.
Rename Ctypes_raw to Ctypes_ptr.
Turn Ctypes_ptr.cptr into an abstract type.
Rename Ctypes_ptr.PtrType to Ctypes_ptr.Raw.
Remove a call to unsafe_raw_addr preceding ctypes_call.
Remove calls to unsafe_raw_addr preceding memcpy.
Remove call to unsafe_raw_addr preceding ctypes_write_pointer.
Remove call to unsafe_raw_addr preceding ctypes_string_of_cstring.
Remove call to unsafe_raw_addr preceding ctypes_string_of_pointer.
Change stub generation to pass fat pointers, not raw pointers, to C.
Pass fat pointers, not raw pointers, to the bigarray view stubs.
Remove calls to unsafe_raw_addr in ptr_diff.
Pass fat pointer, not raw pointer, to ctypes_string_of_array.
Some comments on the inherent lack of safety of raw_address_of_ptr.
Ctypes_bigarray.address ~> unsafe_address, and remove an unused parameter.