Qualify std::ifstream and std::ofstream

Starting with Boost 1.60.0 <boost/filesystem.hpp> includes
<boost/filesystem/fstream.hpp>, which declares ifstream and ofstream
types that make the unqualified names ifstream and ofstream ambiguous.
The names must be qualified to refer to the std versions.

src/pokerth_server.cpp

@@ -161,7 +161,7 @@ main(int argc, char *argv[])
 		pidFile = tmpPidPath.directory_string();
 	}
 	{
-		ofstream pidStream(pidFile.c_str(), ios_base::out | ios_base::trunc);
+		std::ofstream pidStream(pidFile.c_str(), ios_base::out | ios_base::trunc);
 		if (!pidStream.fail())
 			pidStream << getpid();
 		else