Check which classes can be changed to final

[jrfnl]

Tasks:

• Check via GH search if any of the classes are being extended
• For all classes where it could reasonably make sense for them to be extended, leave them be, but make all other classes final.
• Change all protected methods in the final classes to private.

[jrfnl]

I've done the GH searches for this. Please find my findings below. The finding table includes a proposal for select classes to become final. Where the "Make final ?" column is left empty, I'm not sure whether we should or shouldn't make the class final as I want to prevent Requests from becoming too restrictive.

Opinions welcome.

Type	Request 1.x name	Can be final	Make final ?	Search result
class	Requests		no	... ?
class	Requests_Cookie		no	Search results (0)
class	Requests_Exception	X	no	Search results {93,972)
class	Requests_Hooks	X	no	Search results (43,085)
class	Requests_IDNAEncoder		yes no	Search results (0)
class	Requests_IPv6		yes	Search results (0)
class	Requests_IRI		yes no	Search results (0)
class	Requests_Response	X	no	Search results (1)
class	Requests_Session	X	no	Search results (1)
class	Requests_SSL		yes	Search results (0)
class	Requests_Auth_Basic	X	no	Search results (2)
class	Requests_Cookie_Jar		no	Search results (0)
class	Requests_Proxy_HTTP		yes	Search results (0)
class	Requests_Response_Headers		no	Search results (0)
class	Requests_Transport_cURL		yes	Search results (0)
class	Requests_Transport_fsockopen		yes	Search results (0)
class	Requests_Utility_CaseInsensitiveDictionary	X	no	Search results (47,367)
class	Requests_Utility_FilteredIterator		yes	Search results (0)
class	Requests_Exception_HTTP	X	no	Search results (1,561,406)
class	Requests_Exception_Transport	X	no	Search results (46,565)
class	Requests_Exception_Transport_cURL		yes	Search results (0)
class	Requests_Exception_HTTP_###		yes	Search results (0)
class	Requests_Exception_HTTP_Unknown		yes	Search results (0)

New:

Type	New Requests 2.x class	Make final ?
class	Requests\Autoload	yes
class	Requests\Port (upcoming)	yes
class	Requests\Exception\InvalidArgument	yes

Other

All (non-abstract) test classes will also be made final.