tex encoding to mathman now uses encodeURIComponent sans escape

fixes CORE-45

test plan:
- config local canvas to use local mathman
- in equation editor, paste the pound symbol: £
- save the equation
- verify the pound symbol is rendred in the image

Change-Id: I24cfc8788de784e21214c39b65c919b4b2117ff9
Reviewed-on: https://gerrit.instructure.com/132330
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
Product-Review: brian kirkby <bkirkby@instructure.com>
QA-Review: Collin Parrish <cparrish@instructure.com>
Tested-by: Jenkins

app/coffeescripts/views/tinymce/EquationEditorView.coffee

@@ -189,12 +189,20 @@ define [
     restoreCaret: ->
       @editor.selection.moveToBookmark(@prevSelection)
 
+    # the following is here to make it easier to unit test
+    @doubleEncodeEquationForUrl: (text) ->
+      encodeURIComponent encodeURIComponent text
+
+    # the following will be called by onSubmit below
+    doubleEncodeEquationForUrl: (text) ->
+      @constructor.doubleEncodeEquationForUrl text
+
     onSubmit: (event) =>
       event.preventDefault()
 
       text = @getEquation()
       altText = "LaTeX: #{ text }"
-      url = "/equation_images/#{ encodeURIComponent escape text }"
+      url = "/equation_images/#{ @doubleEncodeEquationForUrl text }"
       $img = $(document.createElement('img')).attr
         src: url
         alt: altText

spec/coffeescripts/views/tinymce/EquationEditorViewSpec.coffee

@@ -20,6 +20,14 @@ define [
   'compiled/views/tinymce/EquationEditorView'
 ], ($, EquationEditorView) ->
 
+  QUnit.module "EquationEditorView#doubleEncodeEquationForUrl",
+    setup: ->
+    teardown: ->
+
+  test "encodes pound sign using utf-8", ->
+    equation = "£"
+    equal(EquationEditorView.doubleEncodeEquationForUrl(equation), "%25C2%25A3")
+
   QUnit.module "EquationEditorView#getEquationText",
     setup: ->
     teardown: ->