Synced Makefile.vc6 with recent changes.

Issue posted to the list by malinowsky AT FTW DOT at.
Added winssl-zlib target to VC builds.
xc-am-iface.m4: provide XC_AUTOMAKE macro
configure: automake 1.14 compatibility tweak (use XC_AUTOMAKE)
curl.1: document the --time-cond option in the man page
curl.1: document the --post303 option in the man page
curl.1: document the --sasl-ir option in the man page
Revert "curl.1: document the --time-cond option in the man page"

This reverts commit 3a0e931fc715a80004958794a96b12cf90503f99 because
the documentation of --time-cond was duplicated by mistake.

Reported by: Dave Reisner