Support g++-4.6 in configuration script.

gcc 4.6 doesn't have the -std=c++11 option, it uses the not-yet-finalized
-std=c++0x option.  Use whichever is found to be appropriate at configure
time.
Hookup Travis continous integration test server.
Merge pull request #52 from cscott/travis

Support g++-4.6 and travis CI server.