[Evolution-hackers] Another camel api change

[Not Zed <notzed ximian com>]

Another one that'll affect non-cvs camel providers.

I've moved the provider/provider init stuff into camel-provider.c,
rather than a split between camel-session and camel-provider.  This
means they are no longer per-session, but are truly global.

(should've used the opportunity for resurrecting my experimental camel-
plugin.c, but its too immature).

Api changes:

camel_session_register_provider(session, provider)
 -> camel_provider_register(provider)

camel_session_get_provider(session, url, exception)
 -> camel_provider_get(url, exception)

camel_session_list_providers(session, load)
 -> camel_provider_list(load)

hash = camel_provider_init(void)
 -> void camel_provider_init(void)

camel_provider_load(session, path, ex)
 -> camel_provider_load(path, ex)

And for the module entry point:
camel_provider_module_init(session)
 -> camel_provider_module_init(void)


Also should've addressed re-entrancy of module initialisation, locking
etc.