Add parentheses to avoid possible surprising overflow

If the step size in int_step was not just a number, but
an expression such as 2000000000-1000000000, then doing
"value + step" was more dangerous than "value + (step)".
Some more (documentation) changes to do now.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4924 de43f980-851b-0410-b2f7-c40aca1f87e0
Update 'updated' date of int_step functions

Even though the change in the last commit is minor,
it should be noted.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4925 de43f980-851b-0410-b2f7-c40aca1f87e0