auto update needs "testing version" and handle poor internet connection

[lixun910]

1. For testing purpose, a subversion of minor version (odd number) is introduced. For example.
   release version: 1.8.4
   testing version: 1.8.5 (bug fixe - verify)
   testing version: 1.8.5.1 (bug fixe - verify)
   testing version: 1.8.5.3 (bug fixe - verify)
   ...
   (when testing done)
   release version: 1.8.6

Testers need to enable the "Testing Mode" by checking the box in "About GeoDa" dialog.
Normal users can only get updates of release versions (ends with with even number)

1. With poor internet connection, GeoDa might hangs for about 10 seconds (which is the default response time of LibCurl). This should be addressed.

[jkoschinsky]

Verified in GeoDa 1.8.6.