Const-ify the world (or at least a good part of it)

This patch adds 'const' tags to a number of Asterisk APIs where they are appropriate (where the API already demanded that the function argument not be modified, but the compiler was not informed of that fact). The list includes:

- CLI command handlers
- CLI command handler arguments
- AGI command handlers
- AGI command handler arguments
- Dialplan application handler arguments
- Speech engine API function arguments

In addition, various file-scope and function-scope constant arrays got 'const' and/or 'static' qualifiers where they were missing.

Review: https://reviewboard.asterisk.org/r/251/



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@196072 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/image.h

@@ -51,7 +51,7 @@ int ast_supports_images(struct ast_channel *chan);
  * \retval 0 on success
  * \retval -1 on error
  */
-int ast_send_image(struct ast_channel *chan, char *filename);
+int ast_send_image(struct ast_channel *chan, const char *filename);
 
 /*! 
  * \brief Make an image 
@@ -62,7 +62,7 @@ int ast_send_image(struct ast_channel *chan, char *filename);
  * \retval an ast_frame on success
  * \retval NULL on failure
  */
-struct ast_frame *ast_read_image(char *filename, const char *preflang, int format);
+struct ast_frame *ast_read_image(const char *filename, const char *preflang, int format);
 
 /*! 
  * \brief Register image format