Update messages_en.properties

Fixed a few typos: Mentioning (one n), etc.
Merge pull request #619 from rlheritier/patch-1

Update messages_en.properties
IECompatible: tatam's images on click, mode Ie8
Merge commit '968f4c10aadc56440ca0f65fd50f5043eae24c5c'
Merge branch 'master' of https://github.com/ippontech/tatami into ie8
iPad Compatible: menus correctly shown on iOs 5.0's browser.
IECompatible: tatams with more than 4 images attached
iPad Compatible: slideshow good size for iPad portrait mode
Ie Compatible: Tatams mandatory field error message