Added FPSTR() macro to WString.h

Author: njh

cores/arduino/WString.h

@@ -35,7 +35,8 @@
 //     -std=c++0x
 
 class __FlashStringHelper;
-#define F(string_literal) (reinterpret_cast<const __FlashStringHelper *>(PSTR(string_literal)))
+#define FPSTR(pstr_pointer) (reinterpret_cast<const __FlashStringHelper *>(pstr_pointer))
+#define F(string_literal) (FPSTR(PSTR(string_literal)))
 
 // An inherited class for holding the result of a concatenation.  These
 // result objects are assumed to be writable by subsequent concatenations.