Fix error in PIUtil isValid

The isValid() function was throwing exceptions (rather than gently returning false) when given PIs like nla.obj-134.  We should check for numericity* before trying to decode it as a Long.

*numericity returns search engine results and is therefore a valid word.
Merge remote-tracking branch 'origin/master' into hr-pi-error
Bump to version 1.1.50
Merge pull request #72 from nla/hr-pi-error

Hr pi error