Save as should use default MuseScore format (regression)

Tested using v.0.9.5 RC1

1. Save a file as WAV or some other lossy format
2. Create new score
3. File > Save As

Expected behavior: File should save as Compressed MuseScore file by default

Actual behavior: File actually saves to WAV by default (since that was the previous choice of formats). Although you can easily change the default again I have missed this more than once resulting in accidental data loss (since the WAV file cannot be reopened in MuseScore).

Recommendation: Always default to Compressed MuseScore format (MSCZ) as was the behavior in 0.9.4. This is how Microsoft Word, Inkscape, and almost every software application I can think of works.

History: The behavior was changed at the request of this issue: http://musescore.org/en/node/1742
iDave2 wanted this behavior because he was frequently saving to MusicXML to workaround some other bugs in MuseScore ("MuseScore occasionally made unexpected global changes, far from the measure I was working on. To avoid losing more work, I made frequent saves to XML, then reloaded from XML and started fresh. This process worked better if somewhat awkward." See http://musescore.org/en/node/1727 ). His workflow was non-typical and the change is actually dangerous for the majority of users who intend to use MSCZ. If the "unexpected global changes" iDave2 refers too are still happening they should be filed as a separate bug report.