Improve error handling in nightly when CHPL_NIGHTLY_LOGDIR is not set.

* Report error and exit with non-zero code if CHPL_NIGHTLY_LOGDIR is not set
  (or empty) in -cron mode.
* Try to create the logdir, if it does not exist already (for both -cron and
  -debug modes).
* Check that directory is accessible in both -cron and -debug modes.

Some of these things were already done in -debug mode.
Merge branch 'master' of github.com:chapel-lang/chapel into improve-error-checking-in-nightly
Merge branch 'master' of github.com:chapel-lang/chapel into improve-error-checking-in-nightly
Use "mail" instead of "Mail" as the default nightly testing mailer.

On Ubuntu "Mail" is not provided. On all existing test systems both "mail" and
"Mail" are provided and are the same. Using "mail" as the default will allow
ubuntu testing to use the default instead of having to set CHPL_MAILER.
Test no-local on linux32 instead of gasnet.

32bit clusters are becoming less common and we are really more interested in
testing the linux32 --no-local story.
Merge pull request #799 from thomasvandoren/test-32bit-no-local

Test no-local on linux32 instead of gasnet.

32bit clusters are becoming less common and we are really more interested in
testing the linux32 --no-local story.
Update llvm nightly tests to run spectests.

It turns out nightly does not build the spec tests unless -examples is set. So,
instead of setting the start_test dirs to "release/examples extern/ferguson",
just set extern/ferguson and call nightly with -examples flag.
Merge pull request #802 from thomasvandoren/run-spec-tests-for-llvm

Update llvm nightly tests to run spectests.
Merge pull request #798 from thomasvandoren/update-default-mailer

Use "mail" instead of "Mail" as the default nightly testing mailer.

On Ubuntu "Mail" is not provided. On all existing test systems both "mail" and
"Mail" are provided and are the same. Using "mail" as the default will allow
Ubuntu testing to use the default instead of having to set CHPL_MAILER.
Skip testing m-lsms.par-forall.future on mac/darwin.
Merge pull request #804 from vasslitvinov/skip--m-lsms.par-forall.chpl--on--darwin

Skip testing m-lsms.par-forall.future on mac/darwin.

This test detects a memory error on the mac/darwin -
I updated .future with details.

Also I am skipif-ing this test for darwin so I do not need
to go to the trouble of matching .bad there.
Merge pull request #659 from thomasvandoren/improve-error-checking-in-nightly

Improve error checking in nightly

Add error checks to nightly for the CHPL_NIGHTLY_LOGDIR value that would
have made the issue fixed by #658 easier to realize.