Write our own versions of op= for associative domain set operations instead of relying on the default ones
Add a test for domains with no overlapping indices
Symbolic CHPL_RT_NUM_THREADS_PER_LOCALE values: MAX_PHYSICAL and MAX_LOGICAL.

Add support for two symbolic values for CHPL_RT_NUM_THREADS_PER_LOCALE:
'MAX_PHYSICAL' and 'MAX_LOGICAL'.  These will be interpreted as the
number of physical and logical CPU instances available to the program,
respectively.  Also, add unit tests for these values and as part of
this, introduce a new section of tests/ to contain runtime-specific
tests.
Adding comments stating how set operations on domains handle the removal of indices not present in the LHS domain.
Merge pull request #428 from benharsh/assoc-opeq-fix

Prior to this patch, the op= functions for associative domains were being handled by the generic domain op= functions. Those generic functions don't quite follow the set rules we've decided on. For example, the "-=" operation would halt if the second domain argument did not contain indices that were in the first domain.

Instead, let's write our own op= functions with the desired functionality.

The opEquals.good file is changed as serialization warnings were no longer occurring.
Apply any comm layer maximum thread count.

If the comm layer imposes a maximum thread count, we should apply that
when we've got a symbolic CHPL_RT_NUM_THREADS_PER_LOCALE.
Fix chpl_regexp to use the correct CHPL_TARGET_ARCH value

chpl_regexp was using the displayed target architecture, rather than the
value used in Makefiles. This would cause it to look in the wrong
directory for a re2 install on some platforms.
Merge pull request #429 from gbtitus/symbolic-numthreads-env-var

Support a couple of symbolic CHPL_RT_NUM_THREADS_PER_LOCALE values.

Add support for two symbolic values for CHPL_RT_NUM_THREADS_PER_LOCALE:
'MAX_PHYSICAL' and 'MAX_LOGICAL'. These will be interpreted as the
number of physical and logical CPU instances available to the program,
respectively. Also, add unit tests for these values and as part of
this, introduce a new section of tests/ to contain runtime-specific
tests.

Reviewed by Elliot.
Merge pull request #431 from Kyle-B/kb-chpl-target-arch-re2

Fix chpl_regexp to use the correct CHPL_TARGET_ARCH value

chpl_regexp was using the displayed target architecture, rather than the value used in Makefiles. This would cause it to look in the wrong directory for a re2 install on some platforms.