make code compatible with up-to-date build environment

These changes make it possible to compile open9x with old (avr-gcc 4.3.3, 
avr-libc 1.6.7) and up-to-date (avr-gcc 4.6.2, avr-libc 1.8.0) build
environments. See Issue 1 for more details.

src/pulses.cpp

@@ -215,7 +215,7 @@ FORCEINLINE void setupPulsesPPM()
 }
 
 #if defined(PXX)
-prog_uint16_t APM CRCTable[]=
+pm_uint16_t CRCTable[] PROGMEM =
 {
     0x0000,0x1189,0x2312,0x329b,0x4624,0x57ad,0x6536,0x74bf,
     0x8c48,0x9dc1,0xaf5a,0xbed3,0xca6c,0xdbe5,0xe97e,0xf8f7,