Add isLink functionality

This adds the ability to check within Chapel code if a provided name corresponds
to a soft link.  The interface is visible in the FileSystem module, the
implementation itself lies in chpl-file-utils.c.  Also provide two test cases:
one to exercise files and directories that are and are not links, and one to
exercise the case where the link itself does not exist.
Add timing for each sub_test call.

Register exit handler for sub_test python script that prints the elapsed
seconds from start up to exit (successful exit only). If sub_test is called
without CHPL_ONETEST, e.g. it is called on a directory, it will print a line
like the following when it is complete:

```
[Finished subtest "release/examples" - 16.330 seconds]
```

If sub_test is called with CHPL_ONETEST set, e.g. it is called on a specific
.chpl file, it will print a line like the following when it is complete:

```
[Finished subtest "release/examples/hello" - 2.711 seconds]
```

This will help developers do ad-hoc comparisons of nightly runs as needed. For
example, if a developer things a single test or new suite of tests is adding
significant time to the overall test time, it will be easy to find this line
and compare between two builds.

This is not meant to replace, or even enhance, compiler or runtime performance
tracking that already exists.
Remove a couple of debug lines
Merge branch 'master' of https://github.com/chapel-lang/chapel into add-timing-for-sub-test
Set WARNINGS=1 instead of CHPL_DEVELOPER in nightly.

CHPL_DEVELOPER was added to nightly in commit 06088fc9. Based on internal
notes, it appears CHPL_DEVELOPER was added to enable additional C compiler
warnings. With pull request #594 those warnings can now be enabled by setting
WARNINGS=1 when calling make.
Update CHPL_DEVELOPER.txt docs.
Merge branch 'master' of github.com:chapel-lang/chapel into use-warnings-var-in-nightly

Conflicts:
	doc/developer/bestPractices/CHPL_DEVELOPER.txt
Remove CHPL_DEVELOPER from common.bash.
Add WARNINGS=1 when calling make in smokeTest.
Add support for detecting cray-xe and cray-xc platform.

Look for CLEinfo config file, read it, and inspect the NETWORK value. If it is
"gem", set platform to "cray-xe". If it is "ari", set platform to "cray-xc".

If the CLEinfo file does not exist, or if it does not contain a known NETWORK
value, default to the old platform logic.
fix typos in chpl_platform
Add explicit code to clean up GMP structure when done.
Update README.cray to reflect platform detection on XC and XE.
Merge branch 'master' of github.com:chapel-lang/chapel into better-detect-cray-platform
Add second config to travis that builds with nightly test settings.

There are now two modes that travis will run with each commit:

1) Developer mode: Set CHPL_DEVELOPER=true and call `make check` with no
   additional arguments.

2) Nightly testing mode: Add DEBUG=0 WARNINGS=1 OPTIMIZE=1 when calling `make
   check` like the nightly testing currently does.
Improve smokeTest logging so devs better understand what environment was used.
Fix range
Merge pull request #625 from lydia-duncan/isLink

Add isLink functionality [reviewed by hildeth]

This adds the ability to check within Chapel code if a provided name corresponds
to a soft link. The interface is visible in the FileSystem module, the
implementation itself lies in chpl-file-utils.c. Also provide two test cases:
one to exercise files and directories that are and are not links, and one to
exercise the case where the link itself does not exist.

Tested over std on linux, ran only the new tests on cygwin and darwin to
make sure it worked there, too.
Merge pull request #631 from hildeth/gmpMem

Add explicit code to clean up GMP structures when done.

This was the only remaining test that leaked GMP memory.
Merge pull request #628 from thomasvandoren/use-warnings-var-in-nightly

Set WARNINGS=1 instead of CHPL_DEVELOPER in nightly.

CHPL_DEVELOPER was added to nightly in commit 06088fc. Based on internal
notes, it appears CHPL_DEVELOPER was added to enable additional C compiler
warnings. With pull request #594 those warnings can now be enabled by setting
WARNINGS=1 when calling make.

It is also worth mentioning that start_test explicitly unsets CHPL_DEVELOPER
and adds --cc-warnings flag to the compopts. So, start_test is already running with
backend C compiler warnings.

Also add an additional test configuration to travis. In addition to testing with
CHPL_DEVELOPER=true (developer mode), also test in "nightly test mode". "nightly
test mode" does not set CHPL_DEVELOPER, but it does set DEBUG=0
WARNINGS=1 OPTIMIZE=1 when calling make.