http.c: http.sslcert and http.sslkey are both pathnames

Back when the modern http_options() codepath was created to parse various http.* options at 29508e1e ("Isolate shared HTTP request functionality", 2005-11-18), and then later was corrected for interation between the multiple configuration files in 7059cd99 ("http_init(): Fix config file parsing", 2009-03-09), we parsed configuration variables like http.sslkey, http.sslcert as plain vanilla strings, because git_config_pathname() that understands "~[username]/" prefix did not exist. Later, we converted some of them (namely, http.sslCAPath and http.sslCAInfo) to use the function, and added variables like http.cookeyFile http.pinnedpubkey to use the function from the beginning. Because of that, these variables all understand "~[username]/" prefix. Make the remaining two variables, http.sslcert and http.sslkey, also aware of the convention, as they are both clearly pathnames to files. Noticed-by: Victor Toni <victor.toni@gmail.com> Helped-by: Charles Bailey <cbailey32@bloomberg.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>