[MusicXML] Line style for ties not exported

Discovered using the nightly build - MuseScoreNightly-2014-02-08-1156-1d54c0a.7z - on windows XP.

Steps to reproduce -
1. Create a simple one bar score with a tie and a slur
2. Change the line style for each one to dotted or dashed.
3. Export to MusicXML

The result is that the slur will have the correctly positioned line-type attribute.
<notations>
    <slur line-type="dashed" type="start" number="1"/>
</notations>

However, the tied tag does not contain this attribute - and it should when the line type is not solid.
Like this :
<notations>
    <tied line-type="dashed" type="start" number="1"/>
</notations>