Make example shader metadata conform to new recommendations

I previously checked in OSL Spec changes where, in discussing shader metadata, I replaced some ad-hoc recommendations for nomenclature with recommendations/examples that conform to the metadata conventions of Katana.

This checkin makes the example shaders in src/shaders/*.osl conform to the new recommendations. (And, in a couple places, other extremely minor fix-ups.)

In the process, I found a problem with oslc, wherein it would consider it an error to have metadata whose name masks a global symbol. In particular, if you want to use the recommended "min" and "max" metadata to provide hints about acceptable parameter ranges, you'd get an error about it masking the standard library functions of that name.  So I changed oslc slightly (a one-line fix) to not give this warning in the case of metadata (but still does so for ordinary variables).