Raise error on multiple cout constraints.

In particular, it would be reasonable to expect yield_control.at_least(1).at_most(4).times to work

lib/rspec/matchers/built_in/yield.rb

@@ -98,7 +98,9 @@ def assert_valid_expect_block!
       # Not intended to be instantiated directly.
       class YieldControl < BaseMatcher
         def initialize
+          @already_set = false
           at_least(:once)
+          @already_set = false
         end
 
         # @api public
@@ -182,8 +184,11 @@ def supports_block_expectations?
       private
 
         def set_expected_yields_count(relativity, n)
+          raise "Multiple count constraints are not supported" if @already_set
+
           @expectation_type = relativity
           @expected_yields_count = count_constraint_to_number(n)
+          @already_set = true
         end
 
         def count_constraint_to_number(n)

spec/rspec/matchers/built_in/yield_spec.rb

@@ -73,6 +73,10 @@ def each_arg(*args, &block)
       expect { yield_control.at_most(nil) }.to raise_error(ArgumentError)
     end
 
+    it 'forbids multiple calls to count constraints' do
+      expect { yield_control.at_least(1).at_most(4).times }.to raise_error(/multiple/i)
+    end
+
     context "with exact count" do
       it 'fails if the block yields wrong number of times' do
         expect {