buffer: improve {read,write}{U}Int* methods

Increase the performance and simplify the logic of Buffer#write{U}Int*
and Buffer#read{U}Int* methods by placing the byte manipulation code
directly inline.

Also improve the speed of buffer-write benchmarks by creating a new
call directly to each method by using Function() instead of calling by
buff[fn].

Signed-off-by: Trevor Norris <trev.norris@gmail.com>
node: add signature to SET_PROTOTYPE_METHOD

This prevents segfaults when a native method is reassigned to a
different object (which corrupts args.This()).  When unwrapping,
clients should use args.Holder() instead of args.This().

Closes #6690.

Signed-off-by: Trevor Norris <trev.norris@gmail.com>
lib: use triple equals

Signed-off-by: Trevor Norris <trev.norris@gmail.com>
Merge remote-tracking branch 'upstream/master'