Update the constants associated with the evaluation of j0f(x)
for |x| small.

While here, remove the explicit cast of 0.25 to float.  Replace
a multiplication involving 0.25 by a division using an integer
constant 4.  Make a similar change in j0() to minimize the diff.

Suggested by:	bde


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275518 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f