Add decoding through LibRaw

Decode raw files with LibRaw and fall back to dcraw if LibRaw is unable
to read the file.

rtengine/panasonic_decoders.cc

@@ -58,6 +58,9 @@ unsigned DCraw::pana_bits_t::operator() (int nbits, unsigned *bytes)
     }
 }
 
+namespace
+{
+
 class pana_cs6_page_decoder
 {
     unsigned int pixelbuffer[14], lastoffset, maxoffset;
@@ -99,6 +102,8 @@ void pana_cs6_page_decoder::read_page()
 }
 #undef wbuffer
 
+}
+
 void DCraw::panasonic_load_raw()
 {
     int enc_blck_size = RT_pana_info.bpp == 12 ? 10 : 9;