Use sequence number ranges in pending replies
Use sequence number ranges in pending replies

This allows optimizing adjacent pending replies with the same flags, and
will help support default flags for a range of future requests.

Commit by Josh Triplett and Jamey Sharp.

OpenInkpot-archive/iplinux-libxcb,stapelberg/libxcb,topcat/xcb-win32,OpenInkpot-archive/iplinux-libxcb,topcat/xcb-win32,topcat/xcb-win32,stapelberg/libxcb,stapelberg/libxcb,topcat/xcb-win32,topcat/xcb-win32,OpenInkpot-archive/iplinux-libxcb