Fix startup crash when using a locale boost does not like

There are various locale related bugs in various versions of boost,
where exceptions are thrown in boost::filesystem APIs when the
current locale is not to boost's liking. It's not clear what "not
to boost's liking" means in detail, though "en" and "en_US.UTF-8"
are not to its liking.

Fix it by running a test function that's known to throw in such
a case, and resetting LANG and LC_ALL to C if an exception is
thrown. In simplewallet, the locale is queried before that so the
correct translations will still be used.

src/common/util.h

@@ -88,6 +88,8 @@ namespace tools
    */
   std::error_code replace_file(const std::string& replacement_name, const std::string& replaced_name);
 
+  bool sanitize_locale();
+
   inline crypto::hash get_proof_of_trust_hash(const nodetool::proof_of_trust& pot)
   {
     std::string s;