This fixes backend/chordal2.c.

This fixes opt/boolopt3.c.

This makes them easier to read and avoids markdown interpreting __xxx__
as bold.

This plugs a memory leak.

Thus we only need to maintain the feature list once on the homepage.

This reverts commit 6109afee.
The suffixes were correct before.

The former behaviour was an ad-hoc measure to avoid searching for a free
virtual x87 register. The existence of the NOREG is an ia32 detail
though and does not work with amd64.

This requires changing places which expected the strange behaviour that
querying x87_on_stack finds a slot with the same register, not the slot
with the same node. This is done by x87_reg_on_stack() now.

- Avoid unnecessary const-casts
- Stick to 80 columns

This is more natural than converting a number that cannot be represented
in an unsigned.