Fix a few missing explicit casts

Also fix wrong function return type for Sys_GetCurrentUser
Cmd: Introduce the beginning of a C++ CmdSystem

The API is not fixed yet, there's no doc.
I'm not sure that the completetion is been replaced
correctly.
Fix a few more compile errors on win
Cmd: implement the command buffer + fixes
Fix licensing info for the new files.
The C++ rewrite needs C++11, so bump dependencies accordingly.
More copyright header fixup.
Misleading comment & indentation fixes.
Cvar expansion: no cvar → empty string; no need to test for existence.
Tell travis to use g++ 4.7.
Cmd: move cvar expansion to the command queue
Make travis stop complaining about every failed build.
Cmd: Rename a few functions

"command text" refers to a text containing several commands
"command" refers to a single command
Cmd: add StartsOfCommands
Fix #includes in src/shared.
Allow iterator usage of class Args, e.g. for (auto c : arglist).

Note that the iterator skips the command
You can get one which includes the command by using beginWithCommand().
Convenience return-original-string operator.
Escape the substituted cvar value.
Cmd: try to use more move semantics
Cmd: Remove the need for Cmd::Init()