Upgrade Jetty to 6.1.26

Update the pom.xml to pull Jetty 6.1.26 instead of 6.1.25. There have been a number of bug fixes since .25:

• JETTY-748 Prevent race close of socket by old acceptor threads
• JETTY-1239 HTAccessHandler [allow from 127.0.0.1] does not work
• JETTY-1291 Extract query parameters even if POST content consumed
• JETTY-1293 Avoid usage of String.split
• JETTY-1296 Always clear changes list in selectManager
• JETTY-547 Improved usage of shutdownOutput before close.
• JETTY-912 add per exchange timeout
• JETTY-1051 offer jetty.skip flag for maven plugin
• JETTY-1096 exclude maven and plexus classes from jetty plugin
• JETTY-1248 Infinite loop creating temp MultiPart files
• JETTY-1264 Idle timer deadlock
• JETTY-1271 Handle unavailable request
• JETTY-1278 J2se6 SPI filter handling fix
• JETTY-1283 Allow JSONPojoConvertorFactory to set fromJSON
• JETTY-1287 rewrite handler thread safe issue resolved
• JETTY-1288 info when atypical classloader set to WebAppContext
• JETTY-1289 MRU cache for filter chains
• JETTY-1292 close input streams after keystore.load()
• 325468 Clean work webapp dir before unpack
• 327109 Fixed AJP handling of empty packets
• 327562 Implement all X-Forwarded headers in ProxyServlet