libRETS 1.5.3 released

The following fixes and enhancements are in this version:

• Fix detection of gmcs by configure.
• Fix examples to use lazy initialization of the Columns to better demonstrate how to address just-in-time data delivery.
• Fix Unix perl build.
• Make sure that SearchResultSet::GetColumn doesn't attempt to use an empty string.
• Apply patches provided by Matthew Schultz.
• Default to BOOSTFILESYSTEM3 and boost 1.44 or later. Ticket #166.
• Recognize RETS/1.8.0.
• Pass exceptions through to Java.