Search engine: issue custom fields can now be searched.

Each issue custom field (excepting numeric, date and boolean fields) can be marked as "Searchable" (default to false).

git-svn-id: http://redmine.rubyforge.org/svn/trunk@994 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/fixtures/custom_fields.yml

@@ -11,16 +11,17 @@ custom_fields_001:
   is_required: false
   field_format: list
 custom_fields_002: 
-  name: Build
+  name: Searchable field
   min_length: 1
   regexp: ""
   is_for_all: true
   type: IssueCustomField
-  max_length: 10
+  max_length: 100
   possible_values: ""
   id: 2
   is_required: false
   field_format: string
+  searchable: true
 custom_fields_003: 
   name: Development status
   min_length: 0