Multiple config files are not supported

Problem
-------

OpenDDS currently supports a single configuration file.  Supporting
multiple configuration files would allow complex configurations to be
broken down into more modular configuration files and it allows "base"
configuration to be customized.

Solution
--------

Add a command-line argument named `-DCPSSingleConfigFile 0` to turn on
support for multiple config files.  For backwards compatibility, the
default is `-DCPSSingleConfigFile 0`.  When multiple config files are
enabled, process command-line arguments in order and process each
configuration file as it is encountered.  Multiple configuration files
are supported via multiple `-DCPSConfigFile` arguments.

Configuration now processes environment variables first and then
command-line arguments in order.  Each config file is processed as it
is encounter in the command-line.

dds/DCPS/ConfigStoreImpl.cpp

@@ -1060,7 +1060,6 @@ process_section(ConfigStoreImpl& config_store,
                 const String& key_prefix,
                 ACE_Configuration_Heap& config,
                 const ACE_Configuration_Section_Key& base,
-                const String& filename,
                 bool allow_overwrite)
 {
   // Process the values.
@@ -1077,9 +1076,6 @@ process_section(ConfigStoreImpl& config_store,
           if (config.get_string_value(base, key.c_str(), value) == 0) {
             const String key_name = key_prefix + "_" + ACE_TEXT_ALWAYS_CHAR(key.c_str());
             String value_str = ACE_TEXT_ALWAYS_CHAR(value.c_str());
-            if (value_str == "$file") {
-              value_str = filename;
-            }
             if (allow_overwrite || !config_store.has(key_name.c_str())) {
               config_store.set(key_name.c_str(), value_str);
               if (listener && reader) {
@@ -1125,7 +1121,7 @@ process_section(ConfigStoreImpl& config_store,
     if (status == 0) {
       ACE_Configuration_Section_Key key;
       if (config.open_section(base, section_name.c_str(), 0, key) == 0) {
-        process_section(config_store, reader, listener, next_key_prefix, config, key, filename, allow_overwrite);
+        process_section(config_store, reader, listener, next_key_prefix, config, key, allow_overwrite);
       } else {
         if (log_level >= LogLevel::Error) {
           ACE_ERROR((LM_ERROR,

dds/DCPS/ConfigStoreImpl.h

@@ -261,7 +261,6 @@ process_section(ConfigStoreImpl& config_store,
                 const String& key_prefix,
                 ACE_Configuration_Heap& config,
                 const ACE_Configuration_Section_Key& base,
-                const String& filename,
                 bool allow_overwrite);
 
 } // namespace DCPS