Introduce zend_function_call_entry structure

Instead of directly pushing the zend_function* onto the
function_call_stack, push this structure. This allows us to store
additional data on this stack.
Store arg_num in fcall entry

Instead of storing the argument number in the znode of the parameter
list, store it in fcall->arg_num. This mainly cleans up the parameter
parsing code, which previously had to duplicate all rules (this
becomes more excessive as more features are added, e.g. named params
would already require a minimum of 14 rules...)
Disallow use of positional args after unpacking

This commit disallows the use of trailing positional arguments
after argument unpacking was used. The following calls are no
longer valid:

    fn(...$array, $var);
    fn(...$array1, $var, ...$array2);

However, all of the following continue to be valid:

    fn($var, ...$array);
    fn(...$array1, ...$array2);
    fn($var, ...$array1, ...$array2);

The reason behind this change is a stack allocation issue pointed
out by Dmitry: As of PHP 5.5 the stack necessary for pushing
arguments is precomputed and preallocated, as such the individual
SEND opcodes no longer verify that there is enough stack space.
The unpacked arguments will occupy some of that preallocated
space and as such following positional arguments could write past
a stack page boundary.

An alternative resolution for this issue is to ensure that there
is enough space for the remaining arguments in the UNPACK opcode.
However making this allocation precise (rather than using a
conversative over-estimate) would require some effort. Given that
this particular aspect of the feature wasn't very popular in the
first place, it doesn't seem worth the effort.
Don't add num_additional_args in SEND opcodes

Now that trailing positional args are disallowed,
num_additional_args will always be zero in SEND opcodes (and
FUNC_ARG fetches).
Update stack size in tests/func/010.phpt

Stack size is 16K nowadays. Now the test takes a more reasonable
amount of time to run...