[doc] Fix the parameter names documented for is_permutation - #131

The three-argument is_permutation overload documents a parameter it does not have:

/// \fn is_permutation ( ForwardIterator1 first, ForwardIterator1 last, ForwardIterator2 first2 )
///
/// \param first1   The start of the input sequence
/// \param last2    One past the end of the input sequence     <-- last1
/// \param first2   The start of the second sequence
template< class ForwardIterator1, class ForwardIterator2 >
bool is_permutation ( ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2 )

last2 is not a parameter — it is a local variable computed inside the body (ForwardIterator2 last2 = first2; std::advance(...)), which is presumably how it got into the comment. The four-argument overload twenty lines above documents last1 correctly, so the two overloads describe the same parameter differently.

Both \fn lines in the file also spell the first two parameters first and last, while the declarations use first1 and last1. Doxygen matches \fn against the declaration, so those names should agree too.

Comments only, one file.

Found while sweeping, not included

The same check — every \param/\tparam name in a Doxygen block against the actual signature — turns up a few more in this library and its neighbours:

• boost/algorithm/string/formatter.hpp, empty_formatter documents \param Input while the parameter in the declaration is unnamed (empty_formatter(const RangeT&)).
• Boost.GIL has 42 such mismatches, Boost.Histogram 25, mostly \param names that were renamed in the signature.

I kept this PR to is_permutation. If the rest is worth fixing, say so in a comment and I will send them — per library, so each stays reviewable — or tell me a given one is intentional and I will leave it alone.