[common] cleanup avl and related code
[common] remove unused functions

 - seaf_repo_manager_get_repo_prefix
 - seaf_repo_manager_repo_exists_prefix
[client] land new changes of new-sync for osx
[win] Fix a memory bug when unsyncing a library.
[win] Fix command handling bug in wt-monitor.
Update msi version to 3.1.1.
[win] Fix command handling bug in wt-monitor.
Merge branch 'new-sync-osx' into 3.1
[client] make the compiler happy when compiling with -Wall flag
[client] Fix rename problem on Windows and Mac.

The case is that a file/dir's name changes in cases.
Merge branch 'cleanup_avl' into 3.1
Clean up repo hash table code.
Remove some code with copyright problems.
Remove bitfield code.