boost: fix ambiguous format call on 64-bit builds

Fixes problem:

libs/locale/src/icu/formatter.cpp: In member function
'virtual std::basic_string<_CharT, std::char_traits<_CharT>, std::allocator<_CharT> > boost::locale::impl_icu::number_format<CharType>::format(boost::int64_t, size_t&) const':
libs/locale/src/icu/formatter.cpp:61: error: call of overloaded 'format(boost::int64_t&, icu_49::UnicodeString&)' is ambiguous
/ec/include/unicode/numfmt.h:317: note: candidates are: icu_49::UnicodeString& icu_49::NumberFormat::format(double, icu_49::UnicodeString&) const
/ec/include/unicode/numfmt.h:330: note:                 icu_49::UnicodeString& icu_49::NumberFormat::format(int32_t, icu_49::UnicodeString&) const
/ec/include/unicode/numfmt.h:343: note:                 icu_49::UnicodeString& icu_49::NumberFormat::format(int64_t, icu_49::UnicodeString&) const

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Backported-from: https://svn.boost.org/trac/boost/ticket/6851


diff -ruN boost_1_49_0.orig/libs/locale/src/icu/formatter.cpp boost_1_49_0/libs/locale/src/icu/formatter.cpp
--- boost_1_49_0.orig/libs/locale/src/icu/formatter.cpp 2011-07-12 14:57:36.000000000 +0100
+++ boost_1_49_0/libs/locale/src/icu/formatter.cpp      2012-05-01 14:27:54.000000000 +0100
@@ -58,7 +58,7 @@
             virtual string_type format(int64_t value,size_t &code_points) const
             {
                 icu::UnicodeString tmp;
-                icu_fmt_->format(value,tmp);
+                icu_fmt_->format(::int64_t(value),tmp);
                 code_points=tmp.countChar32();
                 return cvt_.std(tmp);
             }