Fix detect_labview_version when VIKit is not installed

When VIKit is not installed, an "INFO" message should be printed. However,
before this change, several error messages are printed instead.

"The -n test requires that the string be quoted within the test brackets."
From http://tldp.org/LDP/abs/html/comparison-ops.html
Fix testing for VIKit presence

The bash built-in "hash" command is silent when it finds its target, so
testing for a non-zero-length string always passes. Use "which" instead
since it prints the full path to standard out.
Merge pull request #4 from wireddown/windows

Fix testing for the presence of VIKit