Don't perform automatic wildcarding on searches.

Previously a search like function:foo would find all functions that had
"foo" anywhere in their name (like get_foo, set_foo, etc.).  This made
it hard to search for a function called exactly "foo" when there were
many other functions containing that term.

Now function:foo matches only functions called "foo".  Wildcards can be
specified with * and ? characters.  For instance, function:*foo* matches
the old behavior and returns all functions where "foo" appears somewhere
in the name.  Similarly, function:foo* matches functions that begin with
"foo" and function:*foo matches functions that end with "foo".  Using
function:ba? searches for all functions that start with "ba" followed by
exactly one more character so "bar" and "baz" match but "babar" does not.

Open question: should things like function:* be disallowed?