set OOo reference version to 4.1 for incompatible MessageBox changes

This commit:

 http://cgit.freedesktop.org/libreoffice/core/commit/?id=805c6101b3427cc98b53f1c48f22f705206c384d

make LibreOffice 4.2 (and AOO 4.1) widely incompatible to previous
versions. We should thus update the reference version to 4.1 as that is
the version we are least incompatible with. Extension developers are
encouraged to use LibreOffice-minimal-version instead anyway, instead of
the obsolete OOo versioning. see:

 https://wiki.documentfoundation.org/Development/Extension_Development
 https://gerrit.libreoffice.org/gitweb?p=sdk-examples.git;a=commitdiff;h=61f9ca7b18de1adc58cf5d7cb295ba81eb3e5d92;hp=20b8edc74b846db6d143a9e327fb7f7eb2c1fb77

Change-Id: I8275a8244d642100d7b3bc17aa0b12ae7d63e583
Reviewed-on: https://gerrit.libreoffice.org/8852
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>