Add missing import statements.

2 jobs for master in 13 minutes and 36 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #477
java7

00:01:54

passed #476
java8

00:11:41

 
Name Stage Failure
failed
java7 Build There is an unknown failure, please try again
104045 [ERROR] 
104045 [ERROR] Re-run Maven using the -X switch to enable full debug logging.
104045 [ERROR]
104045 [ERROR] For more information about the errors and possible solutions, please read the following articles:
104045 [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException
104045 [ERROR]
104045 [ERROR] After correcting the problems, you can resume the build with the command
104045 [ERROR] mvn <goals> -rf :org.ow2.sat4j.core
ERROR: Job failed: exit code 1