Fix many -Wconversion warnings.

Define my_thread_id as an unsigned type, to avoid mismatch with
ulonglong.  Change some parameters to this type.

Use size_t in a few more places.

Declare many flag constants as unsigned to avoid sign mismatch
when shifting bits or applying the unary ~ operator.

When applying the unary ~ operator to enum constants, explictly
cast the result to an unsigned type, because enum constants can
be treated as signed.

In InnoDB, change the source code line number parameters from
ulint to unsigned type. Also, make some InnoDB functions return
a narrower type (unsigned or uint32_t instead of ulint;
bool instead of ibool).

sql/sql_plugin.h

@@ -1,5 +1,5 @@
 /* Copyright (c) 2005, 2012, Oracle and/or its affiliates.
-   Copyright (c) 2009, 2012, Monty Program Ab
+   Copyright (c) 2009, 2017, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -53,9 +53,9 @@ extern ulong dlopen_count;
 /*
   the following flags are valid for plugin_init()
 */
-#define PLUGIN_INIT_SKIP_DYNAMIC_LOADING 1
-#define PLUGIN_INIT_SKIP_PLUGIN_TABLE    2
-#define PLUGIN_INIT_SKIP_INITIALIZATION  4
+#define PLUGIN_INIT_SKIP_DYNAMIC_LOADING 1U
+#define PLUGIN_INIT_SKIP_PLUGIN_TABLE    2U
+#define PLUGIN_INIT_SKIP_INITIALIZATION  4U
 
 #define INITIAL_LEX_PLUGIN_LIST_SIZE    16
 
@@ -71,12 +71,12 @@ typedef struct st_mysql_show_var SHOW_VAR;
   It's a bitmap, because it makes it easier to test
   "whether the state is one of those..."
 */
-#define PLUGIN_IS_FREED         1
-#define PLUGIN_IS_DELETED       2
-#define PLUGIN_IS_UNINITIALIZED 4
-#define PLUGIN_IS_READY         8
-#define PLUGIN_IS_DYING         16
-#define PLUGIN_IS_DISABLED      32
+#define PLUGIN_IS_FREED         1U
+#define PLUGIN_IS_DELETED       2U
+#define PLUGIN_IS_UNINITIALIZED 4U
+#define PLUGIN_IS_READY         8U
+#define PLUGIN_IS_DYING         16U
+#define PLUGIN_IS_DISABLED      32U
 
 struct st_ptr_backup {
   void **ptr;