Properly ignore alt without ignoring image

* alt_ignore for an image does not ignore the whole image now. If it is missing, it will
  be reported.
* Also, this unearthed another issue, where srcset was not properly 'fixed' by prefixing
  it with http://.

lib/html-proofer/check/images.rb

@@ -37,7 +37,7 @@ def run
         end
       end
 
-      if @img.alt.nil? || (empty_alt_tag? && !@img.ignore_empty_alt?)
+      if !@img.ignore_alt? && (@img.alt.nil? || (empty_alt_tag? && !@img.ignore_empty_alt?))
         add_issue("image #{@img.url} does not have an alt attribute", line: line)
       end
     end

lib/html-proofer/element.rb

@@ -25,6 +25,7 @@ def initialize(obj, check)
       # fix up missing protocols
       @href.insert 0, 'http:' if @href =~ %r{^//}
       @src.insert 0, 'http:' if @src =~ %r{^//}
+      @srcset.insert 0, 'http:' if @srcset =~ %r{^//}
     end
 
     def url
@@ -76,9 +77,9 @@ def ignore?
 
       # ignore user defined URLs
       return true if ignores_pattern_check(@check.options[:url_ignore])
+    end
 
-      # ignore user defined alts
-      return false unless 'ImageCheck' == @type
+    def ignore_alt?
       return true if ignores_pattern_check(@check.options[:alt_ignore])
     end
 

spec/html-proofer/images_spec.rb

@@ -38,6 +38,12 @@
     expect(proofer.failed_tests.first).to match(/failed: response code 0/)
   end
 
+  it 'fails for missing internal images even when alt_ignore is set' do
+    internalImageFilepath = "#{FIXTURES_DIR}/images/missingImageInternal.html"
+    proofer = run_proofer(internalImageFilepath, :file, {:alt_ignore => [/.*/]})
+    expect(proofer.failed_tests.first).to match(/doesnotexist.png does not exist/)
+  end
+
   it 'fails for missing internal images' do
     internalImageFilepath = "#{FIXTURES_DIR}/images/missingImageInternal.html"
     proofer = run_proofer(internalImageFilepath, :file)