If the user had code like "foo.bar" and then entered insert mode after the 'r'
in "bar", YCM would cause vim to hang.
The problem happened because a sorting task was created that would try to sort
on the latest clang result but none would be created because a clang task was
not created in this occasion. clang_data_ready_ would remain false and would
never be set to true, thus causing an infinite loop in SortingThreadMain since
the thread would forever wait on the mutex.
This was rectified with better handling of the clang results cache. Now the
cache is a full class and it also stores the line & column number of the
location for which the results were computed. Better logic is in place for the
cache invalidation.
