Missing assert removal from sdsIncrLen()

Companion for 8eeb1802ec42682a614a5ebca318a0ba44ca7c03, but dealing with hiredis.
Merge pull request #1964 from mariano-perez-rodriguez/patch-2

Missing assert removal from sdsIncrLen()
Missing va_end also added in hiredis copy of sds.c.
Use long for rehash and iterator index in dict.h.

This allows to support datasets with more than 2 billion of keys
(possible in very large memory instances, this bug was actually
reported).

Closes issue #1814.
Cast to right type in dictNext().

This closes issue #1929, the other part was fixed in the context of issue
Fix dictRehash assert casting type.

Also related to #1929.