work around issue in boost::program_options that prevents from compiling in clang

src/util.cpp

@@ -4,6 +4,17 @@
 // file license.txt or http://www.opensource.org/licenses/mit-license.php.
 #include "headers.h"
 #include "strlcpy.h"
+
+// Work around clang compilation problem in Boost 1.46:
+// /usr/include/boost/program_options/detail/config_file.hpp:163:17: error: call to function 'to_internal' that is neither visible in the template definition nor found by argument-dependent lookup
+// See also: http://stackoverflow.com/questions/10020179/compilation-fail-in-boost-librairies-program-options
+//           http://clang.debian.net/status.php?version=3.0&key=CANNOT_FIND_FUNCTION
+namespace boost {
+    namespace program_options {
+        std::string to_internal(const std::string&);
+    }
+}
+
 #include <boost/program_options/detail/config_file.hpp>
 #include <boost/program_options/parsers.hpp>
 #include <boost/filesystem.hpp>