Bump curl version check to 7.19.4 in configure.ac

Constants CURLPROTO_HTTP, CURLPROTO_HTTPS, ... have been introduced in curl 7.19.4.
With current requirement (>= 7.13.1), we would get build errors like
  "cmis/src/libcmis/base-session.cxx:841: error: CURLOPT_PROTOCOLS was not declared in this scope"
in cases of using curl < 7.19.4.

Change-Id: Ifa6c56fc71715cceb19d30bb2d6f48f0b1dbd7da
Reviewed-on: https://gerrit.libreoffice.org/7050Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>

configure.ac

@@ -8675,12 +8675,12 @@ if test "$with_system_curl" = "yes"; then
         curl_version=`$CURLCONFIG --version | $SED -e 's/^libcurl //'`
     fi
 
-    AC_MSG_CHECKING([whether libcurl is >= 7.13.1])
+    AC_MSG_CHECKING([whether libcurl is >= 7.19.4])
 
     case $curl_version in
     dnl brackets doubled below because Autoconf uses them as m4 quote characters,
     dnl so they need to be doubled to end up in the configure script
-    7.13.1|7.1[[4-9]].*|7.[[2-9]]?.*|7.???.*|[[8-9]].*|[[1-9]][[0-9]].*)
+    7.19.4|7.19.[[5-9]]|7.[[2-9]]?.*|7.???.*|[[8-9]].*|[[1-9]][[0-9]].*)
         AC_MSG_RESULT([yes, you have $curl_version])
         ;;
     *)