Added requirements on numeric parameters

[SVN r13460]

include/boost/preprocessor/expr_if.hpp

@@ -17,7 +17,7 @@
 
 /** <p>Expands to <code>EXPR</code> if <code>COND != 0</code> and to nothing if <code>COND == 0</code>.</p>
 
-<p><code>COND</code> must expand to an integer literal.</p>
+<p><code>COND</code> must expand to an integer literal in the range [0, BOOST_PP_LIMIT_MAG].</p>
 
 <p>For example, <code>BOOST_PP_EXPR_IF(1,^)</code> expands to <code>^</code>.</p>