curl: set a 100K buffer size by default

Test command 'time curl http://localhost/80GB -so /dev/null' on a Debian
Linux.

Before (middle performing run out 9):

 real    0m28.078s
 user    0m11.240s
 sys     0m12.876s

After (middle performing run out 9)

 real    0m26.356s (93.9%)
 user    0m5.324s  (47.4%)
 sys     0m8.368s  (65.0%)

Also, doing SFTP over a 200 millsecond latency link is now about 6 times
faster.

Closes #1446

tests/data/test1400

@@ -68,6 +68,7 @@ int main(int argc, char *argv[])
   CURL *hnd;
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "http://%HOSTIP:%HTTPPORT/we/want/1400");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_USERAGENT, "stripped");

tests/data/test1401

@@ -80,6 +80,7 @@ int main(int argc, char *argv[])
   slist1 = curl_slist_append(slist1, "X-Men: cyclops, iceman");
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "http://%HOSTIP:%HTTPPORT/we/want/1401");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_USERPWD, "fake:user");

tests/data/test1402

@@ -73,6 +73,7 @@ int main(int argc, char *argv[])
   CURL *hnd;
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "http://%HOSTIP:%HTTPPORT/we/want/1402");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_POSTFIELDS, "foo=bar&baz=quux");

tests/data/test1403

@@ -70,6 +70,7 @@ int main(int argc, char *argv[])
   CURL *hnd;
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "http://%HOSTIP:%HTTPPORT/we/want/1403?foo=bar&baz=quux");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_USERAGENT, "stripped");

tests/data/test1404

@@ -123,6 +123,7 @@ int main(int argc, char *argv[])
                CURLFORM_END);
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "http://%HOSTIP:%HTTPPORT/we/want/1404");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_HTTPPOST, post1);

tests/data/test1405

@@ -83,6 +83,7 @@ int main(int argc, char *argv[])
   slist3 = curl_slist_append(slist3, "*FAIL HARD");
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "ftp://%HOSTIP:%FTPPORT/1405");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_QUOTE, slist1);

tests/data/test1406

@@ -75,6 +75,7 @@ int main(int argc, char *argv[])
   slist1 = curl_slist_append(slist1, "recipient.two@example.com");
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_INFILESIZE_LARGE, (curl_off_t)38);
   curl_easy_setopt(hnd, CURLOPT_URL, "smtp://%HOSTIP:%SMTPPORT/1406");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);

tests/data/test1407

@@ -57,6 +57,7 @@ int main(int argc, char *argv[])
   CURL *hnd;
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "pop3://%HOSTIP:%POP3PORT/1407");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_DIRLISTONLY, 1L);

tests/data/test1420

@@ -63,6 +63,7 @@ int main(int argc, char *argv[])
   CURL *hnd;
 
   hnd = curl_easy_init();
+  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
   curl_easy_setopt(hnd, CURLOPT_URL, "imap://%HOSTIP:%IMAPPORT/1420/;UID=1");
   curl_easy_setopt(hnd, CURLOPT_HEADER, 1L);
   curl_easy_setopt(hnd, CURLOPT_USERPWD, "user:secret");