BUG: Fixed failure in StataReader when reading variable labels in 117 
Stata's implementation does not match the online dta file format description.
The solution used here is to directly compute the offset rather than reading
it from the dta file.  If Stata fixes their implementation, the original code
can be restored.
closes #7816

anyway to include a test file? (small one)
 I haven't added a test yet, but will do.
 @jreback Test added, so if no typos and all pass, should be ready
 I think it is ready now.
 ok, ping when green
 Strange, a failure in a file I didn't change.
 I think that was fixed
are you rebased against master?
 Rebased
 these look like small test files you created, yes? (which is good)
 @bashtage thanks for the fix!
