(svn r631) Merge r440, r444, r485, r630 to trunk:

r440
Move screenshot function declarations to new file screenshot.h
Clean up screenshot.c a bit, mostly whitespace, alloca() -> malloc() and checking return values
r485
Remove unused field from struct ScreenshotFormat

screenshot.h

@@ -0,0 +1,12 @@
+#ifndef SCREENSHOT_H
+#define SCREENSHOT_H
+
+void InitializeScreenshotFormats(void);
+
+const char *GetScreenshotFormatDesc(int i);
+void SetScreenshotFormat(int i);
+
+bool MakeScreenshot(void);
+bool MakeWorldScreenshot(int left, int top, int width, int height, int zoom);
+
+#endif