Fixed parsing of dependency files (.d) to improve sketch build speed

[cmaglie]

Tested on Windows, this should fix issue #2255.
To be tested on Linux and Mac.

/cc @matthijskooijman

[matthijskooijman]

Looks good to me. Just tested on Linux by moving my sketch dir, aruino install dir and build dir to a complicated path, stuff is still only compiled once. It even works with a header file ending in a space (e.g. 'bar.h '). The .d file looked like this:

/home/matthijs/docs/Electronics/Arduino/Sketches/Test\ $$\ .\ %\ \#\ !\ @\ ZZZ/build/sketch_oct31b.cpp.o: \
 /home/matthijs/docs/Electronics/Arduino/Sketches/Test\ $$\ .\ %\ \#\ !\ @\ ZZZ/build/sketch_oct31b.cpp \
 /home/matthijs/docs/Electronics/Arduino/Sketches/Test\ $$\ .\ %\ \#\ !\ @\ ZZZ/libraries/baz/baz.h \
 /home/matthijs/docs/Electronics/Arduino/Sketches/Test\ $$\ .\ %\ \#\ !\ @\ ZZZ/libraries/baz/bar.h\  \
 /home/matthijs/docs/Electronics/Arduino/Arduino-1.5/buildTest\ $$\ .\ %\ \#\ !\ @\ ZZZ/linux/work/hardware/arduino/avr/cores/arduino/Arduino.h \
(more truncated)

Along with merging this PR, perhaps #2003 also makes sense? That prevents rebuilding core.a when not needed.

[cmaglie]

Thanks for testing this one!

Yes, I'll do a quick review and merge that too.