Improve vim-lldb expression commands for objective-c and implement evaluate-under-cursor:

1. Added new :Lpo command
2. :Lpo and :Lprint can be invoked without parameters. In that case
cursor word will be used
3. Added :LpO command in that case instead of <cword> will be used
stripped <cWORD>. This command is useful for printing objective-c
properties (for ex.: self.tableView). 

Patch by Arthur Evstifeev!!

llvm-svn: 182613