Build environment updates

This pull contains commits to fix the OS X build and allow GitMake test to pass.
Ah. Now I understand why the instructions at the top of the GitConfigure-generated makefile say "N.B. You MUST use -j on FreeBSD." This seems to do with the -B option, which is enabled by default and disabled when -j is present. In other words, it seems '-j 1' in this case forces a single shell instance to run all of the test targets and their commands, rather than a new shell per *command*.

Backing out this change, './GitMake test' by itself breaks. Specifically, './GitMake test_bn' breaks in the way that compelled me to make this change. './GitMake -j 1 -P test_bn' passes. Going back and forth between the two, the test always passes with '-j 1 -P', always breaks without it.

However, I confirmed that this "fix" does create the problem you described. Verified that reverting the change fixes the problem. I'm going to push a rebased branch that omits this particular commit. I'll figure out a better solution to the non-'-j 1 -P' case later, if possible.

A curious note: The '-P' option doesn't exist on FreeBSD 10 or in pmake on Linux. It does exist on bsdmake on OS X.

Thanks for taking a close look, Ben.