Only warn on subclasses of ActiveRecord::Base

in SQL injection, format validation, mass assignment,
and CVE-2010-3933 checks.

Should fix #107

lib/brakeman/checks/check_nested_attributes.rb

@@ -27,7 +27,7 @@ class Brakeman::CheckNestedAttributes < Brakeman::BaseCheck
   end
 
   def uses_nested_attributes?
-    tracker.models.each do |name, model|
+    active_record_models.each do |name, model|
       return true if model[:options][:accepts_nested_attributes_for]
     end
 

lib/brakeman/checks/check_sql.rb

@@ -24,7 +24,7 @@ class Brakeman::CheckSQL < Brakeman::BaseCheck
     end
 
     Brakeman.debug "Finding possible SQL calls on models"
-    calls = tracker.find_call :targets => tracker.models.keys,
+    calls = tracker.find_call :targets => active_record_models.keys,
       :methods => @sql_targets,
       :chained => true
 
@@ -57,7 +57,7 @@ class Brakeman::CheckSQL < Brakeman::BaseCheck
     scope_calls = []
 
     if version_between? "2.1.0", "3.0.9"
-      tracker.models.each do |name, model|
+      active_record_models.each do |name, model|
         if model[:options][:named_scope]
           model[:options][:named_scope].each do |args|
             call = Sexp.new(:call, nil, :named_scope, args).line(args.line)
@@ -66,7 +66,7 @@ class Brakeman::CheckSQL < Brakeman::BaseCheck
         end
        end
     elsif version_between? "3.1.0", "3.9.9"
-      tracker.models.each do |name, model|
+      active_record_models.each do |name, model|
         if model[:options][:scope]
           model[:options][:scope].each do |args|
             second_arg = args[2]

lib/brakeman/checks/check_validation_regex.rb

@@ -15,7 +15,7 @@ class Brakeman::CheckValidationRegex < Brakeman::BaseCheck
   WITH = Sexp.new(:lit, :with)
 
   def run_check
-    tracker.models.each do |name, model|
+    active_record_models.each do |name, model|
       @current_model = name
       format_validations = model[:options][:validates_format_of]
       if format_validations

lib/brakeman/checks/check_without_protection.rb

@@ -14,17 +14,10 @@ class Brakeman::CheckWithoutProtection < Brakeman::BaseCheck
       return
     end
 
-    models = []
-    tracker.models.each do |name, m|
-      if ancestor? m, :"ActiveRecord::Base"
-        models << name
-      end
-    end
-
-    return if models.empty?
+    return if active_record_models.empty?
 
     Brakeman.debug "Finding all mass assignments"
-    calls = tracker.find_call :targets => models, :methods => [:new,
+    calls = tracker.find_call :targets => active_record_models.keys, :methods => [:new,
       :attributes=, 
       :update_attributes, 
       :update_attributes!,