query-parser: special-case wildcards

We were transforming wild-card searches into regular-expression
searches; while that works, it's also significantly slower.

So, instead, special-case wildcards, and use the Xapian machinery for
wildcard queries.

lib/parser/parser.cc

@@ -167,14 +167,9 @@ data (Mux::Tokens& tokens, ProcPtr proc, WarningVec& warnings)
 	}
 
 	// does it look like a regexp?
-	if (val.length()>=2) {
-		if (val[0]=='/' && val[val.length()-1] == '/')
+	if (val.length() >=2 )
+		if (val[0] == '/' && val[val.length()-1] == '/')
 			return regex (fields, val, token.pos, proc, warnings);
-		else if (val[val.length()-1] == '*')
-			return regex (fields, // transfrom wildcard into regexp
-				      "/" + val.substr(0, val.length()-1) + ".*/",
-				      token.pos, proc, warnings);
-	}
 
 	// does it look like a range?
 	const auto dotdot = val.find("..");