Fix locale, charset and filesystem path related issue

Using the "C" locale as default does not cover more "exotic" paths, which can result in exceptions thrown by boost::filesystem::path.

boost::filesystem::path::imbue() returns the "previously used locale", which should be the "right one", if called in a pristine environment, or to put it another way: if imbue() wouldn't be called at all, then this appears to be the one boost::filesystem::path would use.

In this patch, a dummy locale is used to extract the internal locale, to use it explicitly, which seems to be a preferable choice, because the goal is not to modify the locale at all, but to prevent deinitialization issues, and the bad-environment-fallback also kicks in earlier.

src/util.cpp

@@ -713,18 +713,20 @@ void RenameThread(const char* name)
 
 void SetupEnvironment()
 {
-    std::locale loc("C");
     // On most POSIX systems (e.g. Linux, but not BSD) the environment's locale
     // may be invalid, in which case the "C" locale is used as fallback.
 #if !defined(WIN32) && !defined(MAC_OSX) && !defined(__FreeBSD__) && !defined(__OpenBSD__)
     try {
-        loc = std::locale(""); // Raises a runtime error if current locale is invalid
+        std::locale(""); // Raises a runtime error if current locale is invalid
     } catch (const std::runtime_error&) {
         setenv("LC_ALL", "C", 1);
     }
 #endif
-    // The path locale is lazy initialized and to avoid deinitialization errors 
-    // in multithreading environments, it is set explicitly by the main thread.
+    // The path locale is lazy initialized and to avoid deinitialization errors in
+    // multithreading environments, a dummy locale is used to extract the internal
+    // default locale of boost::filesystem::path, which is then used explicitly by
+    // the main thread.
+    std::locale loc = boost::filesystem::path::imbue(std::locale::classic());
     boost::filesystem::path::imbue(loc);
 }