src: fix master build breakage

Fix build breakage with node.js master after the V8 downgrade
from 3.15 to 3.14 in commit joyent/node@b15a10e.

Unconditionally enable the workaround introduced in commit d1ccb29 for
now, 3.14 doesn't have v8::Object::GetAlignedPointerFromInternalField()
or v8::Object::SetAlignedPointerInInternalField().

Fixes #61.