[BUGFIX] cropHTML with dash in html element

Allow dash in regular expression of cropHTML function. It is needed
for recognition of W3C non-standard TYPO3 'link' element syntax.
(e.g. <link email@example.org - mail "Open email window">
email@example.org</link>)

Change-Id: Id7274fdab0be96a9118341a95dab82386d01c903
Fixes: #26915
Releases: 6.0, 4.7, 4.6, 4.5
Reviewed-on: http://review.typo3.org/2641
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Tolleiv Nietsch
Tested-by: Tolleiv Nietsch