Try to detect .m files as Objective-C

They are detected as Octave, but *.m is also used for Objective-C.

src/source.cpp

@@ -103,6 +103,19 @@ Glib::RefPtr<Gsv::Language> Source::guess_language(const boost::filesystem::path
   }
   else if(language->get_id() == "opencl")
     language = language_manager->get_language("cpp");
+  else if(language->get_id() == "octave" && extension == ".m") {
+    // .m is used for both Octave and Objective-C, so try to differentiate
+    std::ifstream input(file_path.string(), std::ios::binary);
+    std::string buffer(256, '\0');
+    input.read(&buffer[0], static_cast<std::streamsize>(buffer.size()));
+    buffer.resize(static_cast<std::size_t>(input.gcount()));
+    if(input && (buffer.find("#import ") != std::string::npos ||
+                 buffer.find("@interface ") != std::string::npos ||
+                 buffer.find("/*") != std::string::npos ||
+                 buffer.find("//") != std::string::npos)) {
+      language = language_manager->get_language("objc");
+    }
+  }
   return language;
 }