Set MACOSX_RPATH property default consistently across CMake versions

The MACOSX_RPATH target property was introduced in CMake 2.8.12, but we
currently allow CMake 2.8.8.  Set CMAKE_MACOSX_RPATH to 0 by default
so that we get consistent behavior across all versions of CMake.
Leave a comment explaining when the default should be updated.

Now that we set a MACOSX_RPATH default explicitly, we no longer need to
set CMake Policy CMP0042 as was added in commit 2ad9f474 (Set CMake
Policies CMP0025 and CMP0042 as necessary, 2014-03-11), so remove it.

Change-Id: I8af24a728379176b9e7ab933206eaa956e1c60f2
ExternalData: Add backtrace to missing file warning

Since commit 32e48028 (If the original file is missing, make it
non-fatal, 2013-10-31) we use a STATUS message instead of a FATAL_ERROR
to report that a DATA{} reference names a missing file.  The STATUS
message has no backtrace.  Use an AUTHOR_WARNING message instead.

Also restore the FATAL_ERROR message when the DATA{} reference names a
file that exists as a directory.

Change-Id: I2cbcb8f6667074401ea9f7743cf6e547ec5061a0
BUGFIX: Add guards for NULL ivars in PrintSelf

The PrintSelf method of vtkStructuredImplicitConnectivity
was causing failures in the otherPrint test b/c it was
dereferencing NULL ivars. Fixed that by adding guards
to chekc if the ivars are NULL.

Change-Id: I50416653e14d5af50a6408c09129f1deebf63ebf
Merge topic 'osx-RPATH-consistency' into master

cd0b6e68 Set MACOSX_RPATH property default consistently across CMake versions
Merge topic 'fix-otherPrint' into master

33920cf2 BUGFIX: Add guards for NULL ivars in PrintSelf
Merge topic 'ExternalData-missing-data-backtrace' into master

94f12816 ExternalData: Add backtrace to missing file warning