Significant REGRESSIONS reformatting/cleanup

To go along with our nice, clean, new cron job identifiers, I've
refactored the REGRESSIONS file, in part inspired by the cleanup, in
part enabled by it.  This doesn't do anything like get us to a
completely happy place with REGRESSIONS, but hopefully people will
understand it better and it'll be useful for regressions week.
(And hopefully after REGRESSIONS week, it'll be much emptier).

There's still more to do here (esp. since not all tests have come
in yet under the new system), but this is a good enough start
that it's worth snapshotting and pushing out for people to see.

The major changes were:

* Updated comments at top of file to reflect current thinking/format

* Reformatted category entries to match nightly runs

* Made the implied/mental inheritance between categories explicit in
  the category header itself rather than vague entries like "along
  with the above"

* Introduced new "wildcard/abstract categories" (other than just
  "general" before) to serve as roots for common configurations
  like "gasnet*" rather than relying on "gasnet-everything" to
  be the base case for all GASNet testing (it wasn't always
  accurate in this respect)

* Tightened up the wording for the category names, reviewed by
  dates, etc. to be pithier.

* Reordered tests to reflect what seems like a more logical ordering:
  Primary environments, interesting configurations, gasnet, xe/xc,
  lower-priority environments, then distribution testing.

* Also tried to unify more on the name "sporadic" when describing
  nondeterministic cases and move these to the end of sections,
  but more work remains here.

Here are some excerpts for reference:

    ===================
    general
    Reviewed 2014-10-16
    ===================
    
    sporadic failure (2-3x a month -- vass)
    ---------------------------------------
    [Error matching program output for parallel/taskPar/taskIntents/21-capture-in-cobegin]


    ...

    ===================
    no-local
    Inherits 'general'
    Reviewed ????-??-??
    ===================


    ===================
    gasnet* regressions
    Inherits 'no-local'
    Reviewed 2014-10-16
    ===================

    annoying occasional failures even after Sung calmed down (09/18/14 -- sungeun)
    ------------------------------------------------------------------------------
    [Error matching program output for types/string/StringImpl/memLeaks/coforall]

    error: cannot create C string from remote string (due to r22900 -- sungeun)
    ---------------------------------------------------------------------------
    [Error matching program output for classes/sungeun/remoteDynamicDispatch (compopts: 1)]
    [Error matching program output for multilocale/diten/needMultiLocales/remoteStringTuple] (due to r23558)
    [Error matching program output for optimizations/sungeun/RADOpt/access1d (compopts: 1)] (2014/06/14)
    [Error matching program output for optimizations/sungeun/RADOpt/access2d (compopts: 1)] (2014/06/14)
    [Error matching program output for optimizations/sungeun/RADOpt/access3d (compopts: 1)] (2014/06/14)
    
    
    ===================
    gasnet-fast
    Inherits 'gasnet*'
    Reviewed ????-??-??
    ===================
    
    noisy failure due to 'slave got an unknown command on coord socket' (09/27/14)
    ------------------------------------------------------------------------------
    [Error matching program output for multilocale/diten/localBlock/needMultiLocales/localBlock5]
    
    noisy unresolved access of range by (2) (10/07/14)
    --------------------------------------------------
    [Error matching program output for users/jglewis/SSCA2_sync_array_initialization_bug]
    
    consistent timeouts
    -------------------
    [Error: Timed out executing program associative/bharshbarg/parSafeAdd (compopts: 1)]
    [Error: Timed out executing program domains/sungeun/assoc/parSafeMember]
    [Error: Timed out executing program memory/shannon/outofmemory/mallocOutOfMemory]
    [Error: Timed out executing program studies/lulesh/sungeun/lulesh (compopts: 1)]
    
    
    
    ================================
    gasnet.linux32
    inherits 'linux32' and 'gasnet*'
    Reviewed 2014-10-16
    ================================

    fairly consistent timeouts due to qthreads oversubscription (09/15/14)
    ----------------------------------------------------------------------
    [Error: Timed out executing program release/examples/benchmarks/hpcc/hpl]
    [Error: Timed out executing program release/examples/benchmarks/hpcc/ptrans]
    [Error: Timed out executing program release/examples/benchmarks/ssca2/SSCA2_main (compopts: 3, execopts: 1)]
    [Error: Timed out executing program release/examples/benchmarks/ssca2/SSCA2_main (compopts: 4, execopts: 1)]
    [Error: Timed out executing program release/examples/benchmarks/ssca2/SSCA2_main (compopts: 5, execopts: 1)]

    sporadic timeout (infrequent)
    -----------------------------
    [Error: Timed out executing program release/examples/benchmarks/ssca2/SSCA2_main (compopts: 2, execopts: 1)]