FIX: Explicit bfs:path conversion to string.

For #25.

src/caosdb/file_transmission/file_reader.cpp

@@ -59,7 +59,7 @@ FileReader::FileReader(boost::filesystem::path filename)
 }
 
 void FileReader::openFile() {
-  stream_.open(filename_, std::ios::binary | std::ios::ate);
+  stream_.open(filename_.generic_string(), std::ios::binary | std::ios::ate);
   if (!stream_) {
     throw FileIOError("Can't open file for reading: " + filename_.string());
   }

src/caosdb/file_transmission/file_writer.cpp

@@ -58,7 +58,7 @@ FileWriter::FileWriter(boost::filesystem::path filename) : filename_(std::move(f
 }
 
 void FileWriter::openFile() {
-  stream_.open(filename_, std::ios::binary | std::ios::trunc);
+  stream_.open(filename_.generic_string(), std::ios::binary | std::ios::trunc);
   if (!stream_) {
     throw FileIOError("Can't open file for writing: " + filename_.string());
   }