Fix EZP-22509: HTML pasted into literal ends up outside literal tag when the
source is not plaintext
Fixed: make sure long lines inside literal tag do not overflow the literal area
Improved the plain text conversion in Firefox when the source is a <pre> tag content
Merge pull request #915 from ezsystems/ezp-22509_paste_outside

EZP-22509: HTML pasted into literal ends up outside literal tag when the source is not plaintext