Convert lookup_symbol_via_quick_fns

This converts lookup_symbol_via_quick_fns to the callback approach,
merging the search loop and the call to expand_symtabs_matching.

Note that this changes lookup_symbol_via_quick_fns to use a
best_symbol_tracker.  Before this patch there was a discrepancy here
between the two search functions.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16994
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16998
Acked-By: Simon Marchi <simon.marchi@efficios.com>