Revert "Change change.c to treat text scale as mils" and fix harder..
This reverts commit
9396377717f7c49cf38d753a35e32d004294b09e and
fixes what was probably the underlying issue... I made a mistake in
commit
2d21a8ad8f38e07b17450450a096f1ce4b3bef0e such that it added
the existing text scale when setting an "absolute" text size, but
ignored it when setting a relative change. (Clearly backwards).
Additionally, I've switched to computing the new value in double
arithmetic to avoid a potential overflow when the input value is
large and we are using a 32-bit Coord type.
See commit
2d21a8ad8f38e07b17450450a096f1ce4b3bef0e for a description
of how text scale is defined and used. If we want to change how our
text is sized / scaled in the future, we would need to change usage
in many more places than the reverted commit touched.