Sort the macro keys by their real-world frequency to reduce the average

Sort the macro keys by their real-world frequency to reduce the average
mask size.  No functional change.

This shrinks the standard /usr/share/man database by 7%, now at 10.3x
the size of whatis.db, and with -Q even by 11%, now at 3.0x of whatis.db.
Now i'm out of ideas to easily shrink the size of the database.

Optimization found somewhere above the West Australian desert.
Committing from Melbourne, Victoria.