Remove accidental use of | in char classes

in these cases, the | was certainly meant as an alternation, but within
a character class, it has no special meaning, so those regexes allowed a
literal | character
Fixed: Empty Content-ID causes strange result -> HTML-tags are "corrupted" (bug#10338).
Squashed commit of the following:

commit e2eff5566a6d9a1d2c23d7639d202e0c042365c2
Author: reneeb <github@renee-baecker.de>
Date:   Fri Mar 7 20:12:56 2014 +0100

    fix test case as method inserts a target attribute

commit 89cc1b15204f4b1c387fe7d659a4e49c58b8193d
Author: reneeb <github@renee-baecker.de>
Date:   Fri Mar 7 16:59:05 2014 +0100

    add test case

commit fbc2f643a617510342a0b38feb6279f8add2a973
Author: reneeb <github@renee-baecker.de>
Date:   Fri Mar 7 15:14:44 2014 +0100

    do not substitute when content-id is empty
Merge remote-tracking branch 'upstream/master' into otrs-master