Fix 608-Tool tooltip display "voidsymbol" if no accelerator is defined

- Add a test on accelerator presence before assign
Update the new Linux build script. Should be functional now.
Linux build: Enable debug mode by default
Fix error: variable length array of non-POD element type 'vector<Gdk::Point>' raised on OSX 10.9
Fix error: cannot pass object of non-POD type 'const synfig::types_namespace::TypeReal::Inner' through variadic function; call will
      abort at runtime
Fix warnings: in-class initializer for static data member of type 'const float' is a GNU extension
Fix more warnings: in-class initializer for static data member of type 'const float' is a GNU extension
Fix warnings: private field not used and unused parameter
Fix more warnings: private field not used and unused parameter
Disable verbose terminate function in OSX. Since 10.9 __gnu_cxx is a unknown namespace
Fix more warnings issued by Clang compiler
Silent remaining warnings triggered by Clang compiler for synfig-core