@chrisdavenport It looks that github think your pull request contains merge conflicts.

@chrisdavenport can you please also fix this file: https://github.com/joomla/joomla-cms/blob/2.5.x/components/com_contact/models/rules/contactemail.php

This can't be merged.

Any idea what the problem is and how to fix it?

You should update your branch to present 2.5.x, and then patch again
I did it manually for contactemail here and I get the following diff. See the difference in the lines:
@@ -23,5 +23,5 @@ vs @@ -22,7 +22,7 @@

diff --git a/components/com_contact/models/rules/contactemail.php b/components/com_contact/models/rules/contactemail.php
index 5904981..a910c01 100644
--- a/components/com_contact/models/rules/contactemail.php
+++ b/components/com_contact/models/rules/contactemail.php
@@ -23,5 +23,5 @@

        foreach(explode(';', $banned) as $item){
-           if ($item != '' && JString::stristr($item, $value) !== false)
+           if (JString::stristr($value, $item) !== false)
                    return false;
        }

while your PR has:

diff --git a/components/com_contact/models/rules/contactemail.php b/components/com_contact/models/rules/contactemail.php
index 875b1e1..bf34f09 100644
--- a/components/com_contact/models/rules/contactemail.php
+++ b/components/com_contact/models/rules/contactemail.php
@@ -22,7 +22,7 @@ public function test(& $element, $value, $group = null, & $input = null, & $form
        $banned = $params->get('banned_email');

        foreach(explode(';', $banned) as $item){
-           if (JString::stristr($item, $value) !== false)
+           if (JString::stristr($value, $item) !== false)
                    return false;
        }

What I did (from memory) is:
On GitHub I forked joomla-cms
On CLI:
git clone
git remote add upstream https://github.com/joomla/joomla-cms.git
git checkout 2.5.x
[made changes to the code]
git add
git commit
git push

What did I miss?

See #4120 for second attempt.

closing in favour of #4120