URI handling: gun and cowlib handle iodata, but shotgun only handles string

[kennethlakin]

As mentioned in the title, gun and cowlib handle iodata URIs, but shotgun does not. Making the change to shotgun required to handle iodata URIs seems to be a safe and compatible thing to do.

cowlib has handled iodata URIs for more than a year ninenines/cowlib@aca97c9#diff-eb68da7989f0e64a350f8ea8707c5b41R283 and the gun manual has mentioned gun's support for iodata URIs for nearly seven months: ninenines/gun@4ae8967#diff-28defa69a935b240f7ac34be244eeb05R165 .

The change will not affect the performance of current shotgun clients that pass in a URI with a leading "/"; a second clause is being added to check_uri to handle iodata and lists whose first element is not "/": kennethlakin@ab6e841#diff-061a9243c5d9756e7d8111fd8f4b4ba7L641

[kennethlakin]

I rebased the branch against master, so I updated my initial comment to point to the new commit and line. The content remains the same.

[kennethlakin]

Merged into master. Yay!