Description:
------------
I can't bind to the _getch() function in msvcrt.dll with FFI. I think this is because it begins with an underscore.

Reproduce code:
---------------
<?php
$z = new FFI("[lib='msvcrt.dll']
    int _getch();
");

while (($c = $z->_getch()) != ord("\r")) {
    $s .= chr($c);
}

print "You typed [$s]\n";

?>


Expected result:
----------------
Something similar to this, which works fine:

<?php
$z = new FFI("[lib='msvcrt.dll']
    int getchar();
");

while (($c = $z->getchar()) != ord("\r")) {
    $s .= chr($c);
}

print "You typed [$s]\n";

?>

Except that the characters wouldn't be echoed to the console, since that's how _getch() works

Actual result:
--------------
Fatal error: Call to undefined method FFI::_getch() in c:\getch.php on line 6

I am thinking that it is the leading underscore in _getch() because of the following code in the default case in parse_defs() in ffi_library.c:

if (isalpha(*c)) {
  while (isalnum(*c) || *c == '_') {
    c++;
  }

This seems to indicate that tokens must start with a letter but then can be alphanumeric or _.