Commands to modify behavior of next call to display-buffer

[bmag]

Add commands to let the user specify on-the-fly how the next invocation of display-buffer should behave. These commands affect only the next invocation. All later invocations of display-buffer use the regular rules. Some ideas for commands:

• no-purpose-on-next-display: next time display-buffer is called, don't use Purpose
• pop-frame-on-next-display: next time display-buffer is called, display the buffer in a new frame
• left-side-on-next-display: next time display-buffer is called, display the buffer in the left side of the current frame/window