Add Doxygen documentation for API changes from 1.6.0 to 1.6.1

Copied from my review board description:
This is a continuation of the API changes documentation started for describing
changes between releases. Most of the API changes were pretty simple needing
only to be brought to attention via the new "Asterisk API Changes" list.
However, if you see anything that needs further explanation feel free to
supplement what is there. The current method of documenting is to add (in the
header file): \version <ver number> <description of changes> and then to add
the function to the change list in doxyref.h on the AstAPIChanges page. I also
made sure all the functions that were newly added were tagged with \since
1.6.1. I think this is a good habit to start both for the historical aspect as
well as for the future ability to easily add a "New Asterisk API" page.

Review: http://reviewboard.digium.com/r/190/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@180719 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/linkedlists.h

@@ -37,7 +37,7 @@
   \retval non-zero on failure
 */
 #define AST_LIST_LOCK(head)						\
-	ast_mutex_lock(&(head)->lock) 
+	ast_mutex_lock(&(head)->lock)
 
 /*!
   \brief Write locks a list.
@@ -62,7 +62,7 @@
 */
 #define AST_RWLIST_RDLOCK(head)                                         \
         ast_rwlock_rdlock(&(head)->lock)
-	
+
 /*!
   \brief Locks a list, without blocking if the list is locked.
   \param head This is a pointer to the list head structure
@@ -73,7 +73,7 @@
   \retval non-zero on failure
 */
 #define AST_LIST_TRYLOCK(head)						\
-	ast_mutex_trylock(&(head)->lock) 
+	ast_mutex_trylock(&(head)->lock)
 
 /*!
   \brief Write locks a list, without blocking if the list is locked.
@@ -98,7 +98,7 @@
 */
 #define AST_RWLIST_TRYRDLOCK(head)                                      \
         ast_rwlock_tryrdlock(&(head)->lock)
-	
+
 /*!
   \brief Attempts to unlock a list.
   \param head This is a pointer to the list head structure
@@ -383,7 +383,7 @@ struct {								\
 }
 
 #define AST_RWLIST_ENTRY AST_LIST_ENTRY
- 
+
 /*!
   \brief Returns the first entry contained in a list.
   \param head This is a pointer to the list head structure
@@ -701,6 +701,7 @@ struct {								\
  * \param elm Pointer to the entry to be inserted
  * \param field Name of the list entry field (declared using AST_LIST_ENTRY())
  * \param sortfield Name of the field on which the list is sorted
+ * \since 1.6.1
  */
 #define AST_LIST_INSERT_SORTALPHA(head, elm, field, sortfield) do { \
 	if (!(head)->first) {                                           \