Windows implementation of QLockFile does not store host name into lock file

See src\corelib\io\qlockfile_win.cpp:101
I suggest using qgetenv("COMPUTERNAME") instead of gethostname(). This will not add dependency of WinSock and should give correct results in most Windows configurations. In worst case (if the environment variable is not set) we will get the same results as in current implementation (empty string).