#187 PATCH_HTTP_KEEPALIVE doc is wrong, it's on by default

[John Hughes]

The doc for SOAP::Constants says that PATCH_HTTP_KEEPALIVE is off by default but examination of the code shows that it's on (in v1.11 and 0.712 at least).

As having it on breaks connection caching -- the patch works badly with at least versions 6.08 and 5.836 of LWP -- this is rather anoying.