Quiet align.chpl errors with Intel and PGI compilers.

The odd behavior on Intel and PGI compilers was due to how a 32-bit temporary was being
inlined:
 - On GCC, the declared size of the temporary (int32_t) was being obeyed, either by being
    written back to a 32-bit memory location, or by being sign-extended inline.
 - On Intel and PGI, the 32-bit result was stored in a 64-bit register and not 32-bit
    sign-extended.

The intent of the test was to demonstrate correct behavior with the first 64-bit integer
not representable as a 32-bit integer.  To avoid compiler dependencies, this constant is
now hard-coded.

The compiler-dependent behavior is captured in a new future with a suggestion for
specifying the behavior that is expected.
Add missing EOL on constOverflow.skipif
Modifications in response to Brad's review.

Use max(int(32)):int(64) + 1 in place of a literal constant.

Removed the "Chapel should ..." phrase.

Added detail to the future, to suggest that runtime overflow checking could be on by
default in debug mode and off by default when optimizations are enabled.
Merge pull request #721 from hildeth/quietAlignErrors

Quiet align.chpl errors on Intel and PGI.

Changed align.chpl to better demonstrate the original intent.
Added a new future to demonstrate the compiler-dependent behavior.