Duplicate SplitStringUsing etc.

[huahang]

The following 2 functions exist in both lmctfy/strings/strutil.cc and lmctfy/strings/split.cc

SplitStringUsing(std::string const&, char const_, std::vector<std::string, std::allocatorstd::string >_)'

SplitStringAllowEmpty(std::string const&, char const_, std::vector<std::string, std::allocatorstd::string >_)

[huahang]

maybe using namespace to guard these functions?

[vmarmol]

It looks like the ones in split.cc are in the strings namespace whereas the ones in strutil are at root. I think strutil should export the ones in split.cc instead, but that will probably require changes in some clients of strutil.