Use the reflected network check on non-Linux platforms

If it has been determined that the reflected check (i.e. using Java 1.6+
code) can be used, then try that first on non-Linux systems.  If it
returns false or cannot be run, then the original Java 1.5 is still
used.

This prevents the network from being detected as down on many non-Linux
systems with Java 1.7.0-b27.

See #10824, #10838, and #11244.

Please do note the following:

* This worked for me on a Windows XP VM with 1.7.0-b27 installed, but please double check that this works across as broad a range of systems as possible.  1.7.0-b27 really must be tested on all platforms, but please do check older Java versions on non-Linux systems as well.
* This is in no way intended to be a comprehensive "make NetworkChecker perfect" PR.  It is a bandage for ticket 11244.  If there is something fundamentally wrong with what is in this PR, I will fix it, but I do not intend to fully address ticket 10824 here.
* Any comments to the effect that this PR does not solve ticket 11244 must be accompanied by the Java version and OS version.

/cc @chris-allan, @jburel, @joshmoore, @bpindelski, @mtbc, @will-moore, @zeb, @rleigh-dundee