Fix redefines of strXXX, original was using strnXXX with length set to 0x7fffffff. This caused problems with strcpy and strcat. The destination buffer was NULL'd to 0x7fffffff which killed the app.
Previous __FlashStringHelper implementation was defines as a char which brought problem in case the method with char* parameter used overloading with __FlashStringHelper* parameter (they was identical). Now __FlashStringHelper is defined as a class and all casts between char* and __FlashStringHelper* are made with reinterpret_cast sugar.
