[3643] Fix problem on Ubuntu and NetBSD Builds

Both Ubuntu and NetBSD builds fail because of what appears to be an error
trying to the use "equal_range" method of one of the classes associated with
the Boost multi-index container. The cause is uncertain - other systems
build successfully, so the problem might no lie here, e.g. it could be in
the compiler.  This fix attempts to side-step the problem by modifying the
affected files so as not to use this method.

src/lib/dhcpsrv/cfg_hosts.cc

@@ -50,13 +50,13 @@ void
 CfgHosts::getAllInternal(const std::vector<uint8_t>& identifier,
                          const Host::IdentifierType& identifier_type,
                          Storage& storage) const {
-    // Search for the Host using the identifier and identifier type as a
-    // composite key.
+    // Use the identifier and identifier type as a composite key.
     const HostContainerIndex0& idx = hosts_.get<0>();
-    std::pair<HostContainerIndex0::iterator, HostContainerIndex0::iterator> r =
-        idx.equal_range(boost::make_tuple(identifier, identifier_type));
+    boost::tuple<const std::vector<uint8_t>, const Host::IdentifierType> t =
+        boost::make_tuple(identifier, identifier_type);
+
     // Append each Host object to the storage.
-    for (HostContainerIndex0::iterator host = r.first; host != r.second;
+    for (HostContainerIndex0::iterator host = idx.lower_bound(t); host != idx.upper_bound(t);
          ++host) {
         storage.push_back(*host);
     }

src/lib/dhcpsrv/cfg_option.h

@@ -303,6 +303,10 @@ public:
     /// name, or an uint32_t value, in which case it specifies a vendor
     /// identifier.
     ///
+    /// @note If there are multiple options with the same key, only one will
+    /// be returned.  No indication will be given of the presence of others,
+    /// and the instance returned is not determinable.
+    ///
     /// @param key Option space name or vendor identifier.
     /// @param option_code Code of the option to be returned.
     /// @tparam Selector one of: @c std::string or @c uint32_t
@@ -312,18 +316,21 @@ public:
     template<typename Selector>
     OptionDescriptor get(const Selector& key,
                          const uint16_t option_code) const {
+
+        // Check for presence of options.
         OptionContainerPtr options = getAll(key);
         if (!options || options->empty()) {
             return (OptionDescriptor(false));
         }
 
+        // Some options present, locate the one we are interested in.
         const OptionContainerTypeIndex& idx = options->get<1>();
-        const OptionContainerTypeRange& range = idx.equal_range(option_code);
-        if (std::distance(range.first, range.second) == 0) {
+        OptionContainerTypeIndex::const_iterator od_itr = idx.find(option_code);
+        if (od_itr == idx.end()) {
             return (OptionDescriptor(false));
         }
 
-        return (*range.first);
+        return (*od_itr);
     }
 
     /// @brief Converts option space name to vendor id.