Fix a bug for handling chpl__tryToken in functionResolution

When rolling back the callStack in functionResolution after a resolution fails
in the then side of a chpl__tryToken conditional, stop if the callStack becomes
empty.

Added a test that causes a compiler segfault without this change because the
callStack becomes empty and then a function is called on the tail of the empty
stack.
Add another multilocale test to lock in chdir's behavior.

This was suggested in response to my file interface proposal.  It verifies that
a chdir() call before the first use of other locales will not affect the current
working directory of the other locales.
Merge pull request #664 from lydia-duncan/additionalChdirTest

Add another multilocale test to lock in chdir's behavior.

This was suggested in response to my file interface proposal. It verifies that
a chdir() call before the first use of other locales will not affect the current
working directory of the other locales.
Add a test of chpl__tryToken that fails to resolve on both branches

Failing on both branches results in an unresolved call error.  Adding this
test was a recommendation from my reviewer (hildeth).
Update .gitignore for new test files

The file utilities functions that Francisco and I have added recently create
stub files and links that don't need to exist in the repository.  After any
test run that includes these directories, git status will flag these files as
untracked.  This will correctly ignore them.
Merge pull request #666 from lydia-duncan/updateGitIgnore

Update .gitignore for new test files

The file utilities functions that Francisco and I have added recently create
stub files and links that don't need to exist in the repository. After any
test run that includes these directories, git status will flag these files as
untracked. This will correctly ignore them.
Improve a comment near tryToken handling code to explain what the tryToken does

Reviewer @hildeth suggested improving on this comment.
Merge pull request #662 from daviditen/callStackBackupOnTryFail

Fix a bug for handling chpl__tryToken in functionResolution
[reviewed by hildeth]

When rolling back the callStack in functionResolution after a resolution fails
in the then side of a chpl__tryToken conditional, stop if the callStack becomes
empty.

Added a test that causes a compiler segfault without this change because the
callStack becomes empty and then a function is called on the tail of the empty
stack.  Added another test showing what happens when both sides of a
conditional using a tryToken fail to resolve (unresolved call error).