Please describe the problem:
When a non-PPT file is renamed as PPT, beagled spews out lot of exceptions. 
Don't be so verbose on exception.  Also return immediately when exception occurs
thus can avoid "Cannot convert to lucene document" exception.

Steps to reproduce:
1. run "beagled --fg --debug"
2. touch ~/sample.ppt
3. 


Actual results:
ERROR: Unable to convert file:///home/varadhan/samples/test-nothing.ppt
(type=File) to a lucene document
ERROR: GLib.GException: No OLE2 signature
in <0x000b1> Gsf.InfileMSOle:.ctor (Gsf.Input)
in [0x0002c] (at
/home/varadhan/cvs/beagle-cvs-02-Mar-2005/Filters/FilterPPT.cs:610)
Beagle.Filters.FilterPPT:DoOpen (System.IO.FileInfo)
in [0x0005b] (at
/home/varadhan/cvs/beagle-cvs-02-Mar-2005/beagled/Filter.cs:378)
Beagle.Daemon.Filter:Open (System.IO.FileInfo)
in [0x000d5] (at
/home/varadhan/cvs/beagle-cvs-02-Mar-2005/beagled/FilteredIndexable.cs:277)
Beagle.Daemon.FilteredIndexable:Build ()
in [0x00001] (at
/home/varadhan/cvs/beagle-cvs-02-Mar-2005/beagled/LuceneDriver.cs:589)
Beagle.Daemon.LuceneDriver:ToLuceneDocument (Beagle.Indexable)
in [0x00223] (at
/home/varadhan/cvs/beagle-cvs-02-Mar-2005/beagled/LuceneDriver.cs:342)
Beagle.Daemon.LuceneDriver:Flush ()


Expected results:
Beagle should display an appropriate error and shouldn't dump the whole stack trace

Does this happen every time?
Yes.

Other information:
Check other filters as well and fix it.