based on a report by Jim Meyering, I went over and added checks for return

codes for all calls to malloc and strdup that were missing. I also changed
a few malloc(13) to use arrays on the stack and a few malloc(PATH_MAX) to
instead use aprintf() to lower memory use.
I also fixed a memory leak in Curl_nss_connect() when CURLOPT_ISSUERCERT is
in use.