systemtime.c: Portably read current time on posix and windows.

w32gdi.c: Implements gamma ramp method for Windows GDI API.
Use double as a cross platform time representation.
Add WinGDI as a selectable method (currently limitied to minimum 4500K).
Fix a bug where redshift would crash if RANDR failed and VidMode wasn't
 compiled in.

src/systemtime.h

@@ -0,0 +1,32 @@
+/* systemtime.h -- Portable system time header
+   This file is part of Redshift.
+
+   Redshift is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   Redshift is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with Redshift.  If not, see <http://www.gnu.org/licenses/>.
+
+   Copyright (c) 2010  Jon Lund Steffensen <jonlst@gmail.com>
+*/
+
+#ifndef _REDSHIFT_SYSTEMTIME_H
+#define _REDSHIFT_SYSTEMTIME_H
+
+#ifndef _WIN32
+# include <time.h>
+#else
+# include <windows.h>
+#endif
+
+
+int systemtime_get_time(double *now);
+
+#endif /* ! _REDSHIFT_SYSTEMTIME_H */