Improvements to the screen capture feature:

Only capture the terminal area, not the margins (if there are any) or
the status bar. Also fixes an issue with odd-sized (width) windows being
saved to .bin files (not supported).
Also, if the current video mode is background-bright (ICE colors), set the
appropriate ANSI flag in the SAUCE record.
Fixed compiler warning (not all paths return a value) in doterm().