imap-send: use cURL automatically when NO_OPENSSL defined

If both USE_CURL_FOR_IMAP_SEND and NO_OPENSSL are defined do
not force the user to add --curl to get a working git imap-send
command.

Instead automatically select --curl and warn and ignore the
--no-curl option.  And while we're in there, correct the
warning message when --curl is requested but not supported.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-imap-send.txt

@@ -44,7 +44,8 @@ OPTIONS
 
 --no-curl::
 	Talk to the IMAP server using git's own IMAP routines instead of
-	using libcurl.
+	using libcurl.  Ignored if Git was built with the NO_OPENSSL option
+	set.
 
 
 CONFIGURATION

imap-send.c

@@ -34,8 +34,16 @@ typedef void *SSL;
 #include "http.h"
 #endif
 
+#if defined(USE_CURL_FOR_IMAP_SEND) && defined(NO_OPENSSL)
+/* only available option */
+#define USE_CURL_DEFAULT 1
+#else
+/* strictly opt in */
+#define USE_CURL_DEFAULT 0
+#endif
+
 static int verbosity;
-static int use_curl; /* strictly opt in */
+static int use_curl = USE_CURL_DEFAULT;
 
 static const char * const imap_send_usage[] = { "git imap-send [-v] [-q] [--[no-]curl] < <mbox>", NULL };
 
@@ -1504,9 +1512,14 @@ int main(int argc, char **argv)
 
 #ifndef USE_CURL_FOR_IMAP_SEND
 	if (use_curl) {
-		warning("--use-curl not supported in this build");
+		warning("--curl not supported in this build");
 		use_curl = 0;
 	}
+#elif defined(NO_OPENSSL)
+	if (!use_curl) {
+		warning("--no-curl not supported in this build");
+		use_curl = 1;
+	}
 #endif
 
 	if (!server.port)