Well I couldn't wait for you till you released a clean core file...so I have made one ;D
It was more for the leaning experience, setting timers, interrupts, pwm etc. Much fun.
I have tested most that I could, no guarantee its bug-free in the first time. 
Its for IDE 0017.
I have the atttiny running @ 8mhz internal xtal.
fuses:
low=0xe2
high=0xdd
extended=0xff
Core file: http://85.12.32.240/~superkoe/arduino/attiny84/attiny84-0.1.zip
extract it in arduino/hardware/cores/
##############################################################
attiny84.name=ATtiny84
attiny84.upload.protocol=stk500
attiny84.upload.maximum_size=8192
attiny84.bootloader.low_fuses=0xe2
attiny84.bootloader.high_fuses=0xdd
attiny84.bootloader.extended_fuses=0xff
attiny84.bootloader.path=attiny84
attiny84.build.mcu=attiny84
attiny84.build.f_cpu=8000000L
attiny84.build.core=attiny84
Add this at the end in programmers.txt in hardware.
The pins: (dip14)
           +-\/-+
       VCC  1|   |14  GND
     (D0) PB0  2|   |13  AREF
     (D1) PB1  3|   |12  PA1 (D9)
      RESET  4|   |11  PA2 (D8)
INT0 Â PWM (D2) PB2 Â 5| Â Â |10 Â PA3 (D7)
   PWM (D3) PA7  6|   |9  PA4 (D6)
   PWM (D4) PA6  7|   |8  PA5 (D5) PWM
          +----+
The PA ports are also analog inputs. so PA0 = 0 and PA7 = 7
The INT0 is the Interrupt port.(there is only 1)