[REVIEW:3-5] fdo#47036 two RTF import fixes

[Miklos Vajna]

Hi,

To fix this regression from 3.4, unfortunately a little refactoring was
unavoidable, so I request cherry-picking of 3 commits:

http://cgit.freedesktop.org/libreoffice/core/commit/?id=de0f331
http://cgit.freedesktop.org/libreoffice/core/commit/?id=0d9132c
http://cgit.freedesktop.org/libreoffice/core/commit/?id=5e994d5

The last two won't apply as-is to -3-5, so I'm attaching the backport of
all three. Testcase in sw/qa/extras/rtftok/data/fdo47036.rtf on master.

Thanks,

Miklos