Minor optimization in the last step of parsing expressions


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4604 de43f980-851b-0410-b2f7-c40aca1f87e0
Use f-expansion rather than x-expansion in fp_set/gset/const.

For floating points, the difference does not matter because none
of the parts of floating points are expandable, but symbolic
expressions (see l3trial/l3fp-symbolic soon) contain expandable
material.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4605 de43f980-851b-0410-b2f7-c40aca1f87e0