Uupdate GSL referenece in packaging script.
Updated libzmq imports to include gssapi.
Updated libsodium imports.
Consolidate shared VS props across versions.
Batched VS builds.
Merge pull request #471 from evoskuil/master

Batch VS builds, consolidate shared props, update imports
Use gsl vs. gslgen for batch model builds.
Harden MSBUILD base script against various VS installations.
Optimize VS projects and common props.
Merge pull request #472 from evoskuil/master

Simplify VS project configs and harden MSBUILD script
Sort project.xml and regenerate.
Generating VS 2010/2012 models from master, whitespace difference.
VS props cloning across versions missed two files.
Cast void* to return type.
Conditionally disable non-portable code.
Merge pull request #473 from evoskuil/master

VS project updates, sort source files, Windows fixes for new code.
Whitespace fixes
Thread local storage on gcc uses __thread
Problem: _test methods are not consistent

CLASS RFC specifies void methods; if a test fails the code should
abort. There is no semantic for returning an error code. However
many of the classes used an int type for their test method.

Solution: change all those classes to use a void method.
Added zfile_has_changed() method & test