Fixes clang compiler bug in argument deduction

[stefan-it]

This PR fixes a clang compiler bug in argument deduction:

....
test_binary.cpp:51:17: error: call to 'load' is ambiguous
    auto t_in = usb::load<T>(is);
                ^~~~~~~~~~~~
./load.hpp:31:7: note: candidate function [with T = std::__cxx11::basic_string<char>, $1 = <>]
    T load(std::ifstream& in) {
      ^
./load.hpp:37:7: note: candidate function [with T = std::__cxx11::basic_string<char>, $1 = <>]
    T load(std::ifstream& in) {
      ^
./load.hpp:43:7: note: candidate function [with T = std::__cxx11::basic_string<char>, $1 = <>]
    T load(std::ifstream& in) {
      ^
./load.hpp:49:7: note: candidate function [with T = std::__cxx11::basic_string<char>, $1 = <>]
    T load(std::ifstream& in) {
      ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.

See [1] for further information. With this patch compilation on clang with the latest version 3.8 works without problems, tested on Arch Linux:

$ clang++ --version
clang version 3.8.1 (tags/RELEASE_381/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
$ rake
clang++ -std=c++11 -Wall -Wextra test_binary.cpp -o test_binary.test
./test_binary.test
All tests run successful.

[1] https://llvm.org/bugs/show_bug.cgi?id=11723

[xdbr]

oh thanks @stefan-it! i will need to have a closer look at this before merging it in, hope to get to it soon!