support spaces in file names during compile

Hey Josh,

Under linux avr-g++ fails when passed a sketch with spaces in the name.
```
/home/sam/ElectronIDE/downloads/platforms/1.0.5/linux/hardware/tools/avr/bin/avr-g++ -c -g -Os -Wall -fno-exceptions -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L -MMD -DARDUINO=105 -DUSB_VID=0x2341 -DUSB_PID=0x0043 -I/home/sam/ElectronIDE/downloads/platforms/1.0.5/linux/hardware/arduino/cores/arduino -I/home/sam/ElectronIDE/downloads/platforms/1.0.5/linux/hardware/arduino/variants/standard -I/home/sam/ownCloud/Electronics/sketchbook/Simple Onboard Blinker build/tmp/Simple Onboard Blinker.cpp -o build/out/Simple Onboard Blinker.cpp.o
avr-g++: Onboard: No such file or directory
avr-g++: Blinker: No such file or directory
avr-g++: build/tmp/Simple: No such file or directory
avr-g++: Onboard: No such file or directory
avr-g++: Blinker.cpp: No such file or directory
avr-g++: Onboard: No such file or directory
avr-g++: Blinker.cpp.o: No such file or directory
avr-g++: no input files
```
I had a shot at fixing this, i'm pretty new to Node though. Seems to work.

Cheers,
Sam.