Fixed missing NOT_AN_INTERRUPT constant in digitalPinToInterrupt()

Fixes #2379
Revert "Match return value to type in available()"

This reverts commit f40e4713542fa862d5b99b256a642e001a796988.
Added an hint for the buffer sizes.

See #2057
Fixes #2367
Updated revision log
Merge branch 'master' into ide-1.5.x

Conflicts:
	hardware/arduino/cores/arduino/HardwareSerial.cpp
	hardware/arduino/cores/robot/Arduino.h