Catch incorrect usage of esc_attr__()

[gudmdharalds]

For instance:

 <a href="..."><?php echo esc_attr__( 'testing', 'mytheme' ); ?> </a>

[GaryJones]

We check if esc_html() is being used in an attribute, but we don't check if esc_attr() (or the variants) are being used outside of an attribute.