Allow multiple comparisons in int/dim_compare (see #106)

Now \int_compare_p:n { 0 <= \l_my_int != 10 } checks
that \l_my_int is non-negative, but different from 10.
Specifically,

  \(int|dim)_compare_p:n
    { <expr_1> <rel_1> ... <expr_N> <rel_N> <expr_{N+1}> }

is true if all comparisons <expr_i> <rel_i> <expr_{i+1}>
are true.  Evaluation is lazy: as soon as one comparison is
false, we stop evaluating.  There remains to do fp_compare.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4444 de43f980-851b-0410-b2f7-c40aca1f87e0