I’ve been using  org.apache.poi.hsmf.MAPIMessage to handle reading the contents
of Outlook MSG files and I noticed that for some reason there was no accessor
method for getting at the “FROM” field.

I’m not sure if this was omitted for a reason but its absence seemed strange so
I decided to try and add it.

I gleaned from the HSMF javadoc that the various fields in a MSG file can be
identified by looking for OLE nodes with the following name

__substg1.0_<chunk_id><chunk_type>

Where <chunk_type> is an arbitrary HEX code indicating what data type the
property has and <chunk_id> is an arbitrary HEX code that identifies each property.

I did some searching through some sample MSG files and narrowed down the FROM
field to one of the following two chunk Ids:  0x0042 or 0x0C1A
Both seemed to work equally well in the files I tested on.

This patch contains the following changes:

-	Added “displayFromChunk” to instance to org.apache.poi.hsmf.datatypes.Chunks
-	Added “getDispalyFrom” accessor method to org.apache.poi.hsmf.MAPIMessage
-	Added a method to org.apache.poi.hsmf.model.TestBlankFileRead to test reading
the “FROM” field
-	Added a method to org.apache.poi.hsmf.model.TestSimpleFileRead to test reading
the “FROM” field

I also added an overloaded constructor to MAPIMessage that takes in an
InputStream (as opposed to just a file name).  This change had nothing to do
with the accessing the “FROM” field but was useful for the interface I was
implementing and didn’t seem to cost anything in terms of extra complexity in
the code.