Add 100% line/branch coverage to rack/query_parser.rb

Remove dead code in _normalize_params. There are two different types of
dead code.  First, directly before this dead code, you have
`v ||= String.new`, so `!v.nil?` is always true and could be removed.
The remaining conditions for the dead branch are `k.empty?` and
`name = '[]'`. Looking at the conditional above, it's never possible
for these two conditions to be simultaneously true:

```ruby
if !name
  # name != '[]'
elsif depth == 0
  if start = name.index('[', 1)
    k = name[0, start]
    # !k.empty?
  else
    k = name
    # !k.empty? || name != '[]'
  end
elsif name.start_with?('[]')
  k = '[]'
  # !k.empty?
else # all remaining branches
  # name != '[]', otherwise previous branch taken
end
```

Coverage after this commit:

3283 relevant lines, 3282 lines covered and 1 lines missed. ( 99.97% )
1112 total branches, 1068 branches covered and 44 branches missed. ( 96.04% )

1 files changed, 8 insertions, 0 deletions

diff --git a/test/spec_utils.rb b/test/spec_utils.rb
index 90df2e27..6b75e2ef 100644
--- a/test/spec_utils.rb
+++ b/test/spec_utils.rb
@@ -131,6 +131,14 @@ describe Rack::Utils do
     Rack::Utils.parse_nested_query(nil).must_equal({})
   end
 
+  deprecated "should warn for deprecated QueryParser.make_default call with key_space_limit" do
+    Rack::QueryParser.make_default(1, 1).must_be_kind_of Rack::QueryParser
+  end
+
+  deprecated "should warn using deprecated QueryParser.new call with key_space_limit" do
+    Rack::QueryParser.new(Rack::QueryParser::Params, 1, 1).must_be_kind_of Rack::QueryParser
+  end
+
   deprecated "should warn using deprecated Rack::Util.key_space_limit=" do
     Rack::Utils.key_space_limit = 65536
   end