select/cray: handling errors in do_basil_release()

This reduces the amount of error text printed on failure of do_basil_release():
 * parameter failures are caught by the existing calls to error(),
 * internal (ALPS) errors are printed by basil_release(),
 * there is no need to return additional error information via errno,
 * functions calling select_g_job_fini() just interpret the error, but no
   further action is taken, hence it is not necessary to indicate failure
   more than once.

The following shows how setting SLURM_ERROR/errno produces unnecessarily long error text:

 [2011-02-09T18:19:51] debug2: Processing RPC: REQUEST_CANCEL_JOB_STEP uid=21215
 [2011-02-09T18:19:51] error: PERMANENT ALPS BACKEND error: ALPS error: apsched: No entry for resId 286
 [2011-02-09T18:19:51] error: releasing ALPS resId 286 for JobId 2940 FAILED with -5
 [2011-02-09T18:19:51] error: select_g_job_fini(2940): No error

With the patch, only						       
 [2011-02-09T18:19:51] error: PERMANENT ALPS BACKEND error: ALPS error: apsched: No entry for resId 286
would be printed, which is sufficient to diagnose the problem (resId 286 had been
terminated by ALPS internally, after not receiving a confirmation quickly enough).