Fix in-source builds

The internal header directory conflicted with in-source builds causing a
build failure. This is fixed by renaming the internal header directory to
something other than maxscale.

The renaming pointed out a few problems in a couple of source files that
appeared to include internal headers when the headers were in fact public
headers.

Fixed maxctrl in-source builds by making the copying of the sources
optional.

server/core/internal/modules.h

@@ -0,0 +1,154 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+/**
+ * @file modules.h  Utilities for loading modules
+ */
+
+#include <maxscale/cdefs.h>
+#include <maxscale/dcb.h>
+#include <maxscale/modinfo.h>
+#include <maxscale/resultset.h>
+#include <maxscale/debug.h>
+
+MXS_BEGIN_DECLS
+
+/**
+ * Module types
+ */
+#define MODULE_PROTOCOL         "Protocol"        /**< A protocol module type */
+#define MODULE_AUTHENTICATOR    "Authenticator"   /**< An authenticator module type */
+#define MODULE_ROUTER           "Router"          /**< A router module type */
+#define MODULE_MONITOR          "Monitor"         /**< A database monitor module type */
+#define MODULE_FILTER           "Filter"          /**< A filter module type */
+#define MODULE_QUERY_CLASSIFIER "QueryClassifier" /**< A query classifier module type */
+
+
+/**
+ *@brief Load a module
+ *
+ * @param module Name of the module to load
+ * @param type   Type of module, used purely for registration
+ * @return       The module specific entry point structure or NULL
+ */
+void *load_module(const char *module, const char *type);
+
+/**
+ * @brief Get a module
+ *
+ * @param name Name of the module
+ * @param type The module type or NULL for any type
+ * @return The loaded module or NULL if the module is not loaded
+ */
+const MXS_MODULE *get_module(const char *name, const char *type);
+
+/**
+ * @brief Unload a module.
+ *
+ * No errors are returned since it is not clear that much can be done
+ * to fix issues relating to unloading modules.
+ *
+ * @param module The name of the module
+ */
+void unload_module(const char *module);
+
+/**
+ * @brief Unload all modules
+ *
+ * Remove all the modules from the system, called during shutdown
+ * to allow termination hooks to be called.
+ */
+void unload_all_modules();
+
+/**
+ * @brief Print Modules
+ *
+ * Diagnostic routine to display all the loaded modules
+ */
+void printModules();
+
+/**
+ * @brief Print Modules to a DCB
+ *
+ * Diagnostic routine to display all the loaded modules
+ */
+void dprintAllModules(DCB *);
+
+/**
+ * @brief Return a resultset that has the current set of modules in it
+ *
+ * @return A Result set
+ */
+RESULTSET *moduleGetList();
+
+typedef struct mxs_module_iterator
+{
+    const char* type;
+    void* position;
+} MXS_MODULE_ITERATOR;
+
+/**
+ * @brief Returns an iterator to modules.
+ *
+ * @attention It is unspecified whether a module loaded after the iterator
+ *            was created, will be returned by the iterator. The behaviour
+ *            is undefined if a module is unloaded while an iteration is
+ *            being performed.
+ *
+ * @param type  The type of modules that should be returned. If NULL,
+ *              then all modules are returned.
+ *
+ * @return An iterator.
+ */
+MXS_MODULE_ITERATOR mxs_module_iterator_get(const char* type);
+
+/**
+ * @brief Indicates whether the iterator has a module to return.
+ *
+ * @param iterator  An iterator
+ *
+ * @return True if a subsequent call to @c mxs_module_iterator_get
+ *         will return a module.
+ */
+bool mxs_module_iterator_has_next(const MXS_MODULE_ITERATOR* iterator);
+
+/**
+ * @brief Returns the next module and advances the iterator.
+ *
+ * @param iterator  An iterator.
+ *
+ * @return A module if there was a module to return, NULL otherwise.
+ */
+MXS_MODULE* mxs_module_iterator_get_next(MXS_MODULE_ITERATOR* iterator);
+
+/**
+ * @brief Convert module to JSON
+ *
+ * @param module Module to convert
+ * @param host   Hostname of this server
+ *
+ * @return The module in JSON format
+ */
+json_t* module_to_json(const MXS_MODULE* module, const char* host);
+
+/**
+ * @brief Convert all modules to JSON
+ *
+ * @param host The hostname of this server
+ *
+ * @return Array of modules in JSON format
+ */
+json_t* module_list_to_json(const char* host);
+
+MXS_END_DECLS