added  -D__PROG_TYPES_COMPAT__ to the avr-g++ compiler flags

this results in just a deprecated warning rather than an error when using libraries that still use prog_XXX types

this is how the IDE does it:

```
/usr/share/arduino/hardware/tools/avr/bin/avr-g++ -c -g -Os -Wall -fno-exceptions -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=8000000L -MMD -DUSB_VID=null -DUSB_PID=null -DARDUINO=105 -D__PROG_TYPES_COMPAT__ -I/usr/share/arduino/hardware/arduino/cores/arduino ......blah
```
and means that libraries don't have to add the ```#define __PROG_TYPES_COMPAT__``` line.

References:
http://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html
https://github.com/jcw/jeelib/commit/f21ac03