schema: add NAME_LENGTH constant

It's probably not the best place for this constant, but that's where
it is in origin.

Signed-off-by: Paweł Dziepak <pdziepak@cloudius-systems.com>

schema.cc

@@ -8,6 +8,8 @@
 #include "schema_builder.hh"
 #include <boost/algorithm/cxx11/any_of.hpp>
 
+constexpr int32_t schema::NAME_LENGTH;
+
 template<typename Sequence>
 std::vector<data_type>
 get_column_types(const Sequence& column_definitions) {

schema.hh

@@ -169,6 +169,8 @@ public:
     typedef boost::iterator_range<iterator> iterator_range_type;
     typedef boost::iterator_range<const_iterator> const_iterator_range_type;
 
+    static constexpr int32_t NAME_LENGTH = 48;
+
     struct column {
         bytes name;
         data_type type;