Include 'build info' in all --version text and About boxes.

Include 'build info' in all --version text and About boxes.

This shows the build platform (32- vs 64-bit in particular, and also
whether Unix GTK builds were compiled with or without the X11 pieces),
what compiler was used to build the binary, and any interesting build
options that might have been set on the make command line (especially,
but not limited to, the security-damaging ones like NO_SECURITY or
UNPROTECT). This will probably be useful all over the place, but in
particular it should allow the different Windows binaries to be told
apart!

Commits 21101c739 and 2eb952ca3 laid the groundwork for this, by
allowing the various About boxes to contain free text and also
ensuring they could be copied and pasted easily as part of a bug
report.