EggsFS -> TernFS rename

Things not done because probably disruptive:

* kmod filesystem string
* sysctl/debugfs/trace
* metrics names
* xmon instance names

Some of these might be renamed too, but starting with a relatively
safe set.

cpp/core/Exception.cpp

@@ -178,7 +178,7 @@ std::string removeTemplates(const std::string & s) {
 
 }
 
-const char *EggsException::what() const throw() {
+const char *TernException::what() const throw() {
     return _msg.c_str();
 }