Improved fields dependence (show/hide) in backend's config section

[luigifab]

Description

This fix display of customized elements when a field depend on another one.

Manual testing scenarios

First, update app/code/core/Mage/Page/etc/system.xml like this:

diff --git a/app/code/core/Mage/Page/etc/system.xml b/app/code/core/Mage/Page/etc/system.xml
index 635353f637..88c1aba8c7 100644
--- a/app/code/core/Mage/Page/etc/system.xml
+++ b/app/code/core/Mage/Page/etc/system.xml
@@ -37,6 +37,15 @@
                     <show_in_website>1</show_in_website>
                     <show_in_store>1</show_in_store>
                     <fields>
+                        <yesno>
+                            <label>yesno</label>
+                            <frontend_type>select</frontend_type>
+                            <source_model>adminhtml/system_config_source_yesno</source_model>
+                            <sort_order>4</sort_order>
+                            <show_in_default>1</show_in_default>
+                            <show_in_website>1</show_in_website>
+                            <show_in_store>1</show_in_store>
+                        </yesno>
                         <shortcut_icon translate="label comment">
                             <label>Favicon Icon</label>
                             <comment>Allowed file types: ICO, PNG, GIF, JPG, JPEG, APNG. Not all browsers support all these formats!</comment>
@@ -47,6 +56,7 @@
                             <show_in_default>1</show_in_default>
                             <show_in_website>1</show_in_website>
                             <show_in_store>1</show_in_store>
+                            <depends><yesno>1</yesno></depends>
                         </shortcut_icon>
                         <default_title translate="label">
                             <label>Default Title</label>

Go to System / Configuration / Design / HTML head:

Here, there are no problems with the favicon, when the select is yes or no.

But... if you customize the element and add some html tags, like for example by adding in app/code/core/Mage/Adminhtml/Block/System/Config/Form/Field/Image.php:

    public function getElementHtml() {
        return '<div style="background-color:yellow;">'.parent::getElementHtml().'</div>';
    }

No:

Yes:

Apply the PR, then try again No:

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[fballiano]

tested and I couldn't find anything not working

[kiatng]

Tested. I removed an extra semicolon.