sanitize the OpenSSL detection

configure.in

@@ -17,25 +17,59 @@ AC_SUBST(SOCK_LIBS)
 
 m4_ifdef([AS_HELP_STRING], , [m4_define([AS_HELP_STRING], m4_defn([AC_HELP_STRING]))])
 
-ssl=false
+have_ssl_paths=
 AC_ARG_WITH(ssl,
-  AS_HELP_STRING([--with-ssl=DIR], [yes/no/OpenSSL installation root [detect]]),
+  AS_HELP_STRING([--with-ssl[=PATH]], [where to look for SSL [detect]]),
   [ob_cv_with_ssl=$withval])
 if test "x$ob_cv_with_ssl" != xno; then
-    if test -d "$ob_cv_with_ssl/lib"; then
-      CPFLAGS="$CPPFLAGS -I$ob_cv_with_ssl/include"
-      LDFLAGS="$LDFLAGS -L$ob_cv_with_ssl/lib"
+  case $ob_cv_with_ssl in
+    ""|yes)
+      dnl Detect the pkg-config tool, as it may have extra info about the openssl
+      dnl installation we can use. I *believe* this is what we are expected to do
+      dnl on really recent Redhat Linux hosts.
+      AC_PATH_PROG(PKGCONFIG, pkg-config, no, $PATH:/usr/bin:/usr/local/bin)
+      if test "$PKGCONFIG" != "no" ; then
+        AC_MSG_CHECKING([OpenSSL presence with pkg-config])
+        if $PKGCONFIG --exists openssl; then
+          SSL_LIBS=`$PKGCONFIG --libs-only-l openssl`
+          SSL_LDFLAGS=`$PKGCONFIG --libs-only-L openssl`
+          SSL_CPPFLAGS=`$PKGCONFIG --cflags-only-I openssl`
+          have_ssl_paths=yes
+          AC_MSG_RESULT([found])
+        else
+          AC_MSG_RESULT([not found])
+        fi
       fi
-    AC_CHECK_LIB(crypto, ERR_error_string, [cryptolib=" -lcrypto"])
-    AC_CHECK_LIB(ssl, SSL_library_init, [
-	SSL_LIBS="-lssl$cryptolib"
-	AC_DEFINE(HAVE_LIBSSL, 1, [Define if you want SSL support])
-	ssl=true
-      ],[
+      ;;
+    *)
+      SSL_LDFLAGS=-L$ob_cv_with_ssl/lib$libsuff
+      SSL_CPPFLAGS=-I$ob_cv_with_ssl/include
+      ;;
+  esac
+  if test -z "$have_ssl_paths"; then
+    sav_LDFLAGS=$LDFLAGS
+    LDFLAGS="$LDFLAGS $SSL_LDFLAGS"
+    AC_CHECK_LIB(dl, dlopen, [LIBDL=-ldl])
+    AC_CHECK_LIB(crypto, CRYPTO_lock, [LIBCRYPTO=-lcrypto])
+    AC_CHECK_LIB(ssl, SSL_connect,
+                 [SSL_LIBS="-lssl $LIBCRYPTO $LIBDL" have_ssl_paths=yes])
+    LDFLAGS=$sav_LDFLAGS
+  fi
+
+  sav_CPPFLAGS=$CPPFLAGS
+  CPPFLAGS="$CPPFLAGS $SSL_CPPFLAGS"
+  AC_CHECK_HEADER(openssl/ssl.h, , [have_ssl_paths=])
+  CPPFLAGS=$sav_CPPFLAGS
+
+  if test -z "$have_ssl_paths"; then
     if test -n "$ob_cv_with_ssl"; then
-	    AC_MSG_ERROR([can't find OpenSSL])
+      AC_MSG_ERROR([OpenSSL libs and/or includes were not found where specified])
+    fi
+  else
+    AC_DEFINE(HAVE_SSL, 1, [if you have the OpenSSL libraries])
+    CPPFLAGS="$CPPFLAGS $SSL_CPPFLAGS"
+    LDFLAGS="$LDFLAGS $SSL_LDFLAGS"
   fi
-      ])
 fi
 AC_SUBST(SSL_LIBS)
 
@@ -61,7 +95,7 @@ AM_CONDITIONAL(with_compat, test "x$ob_cv_enable_compat" != xno)
 
 AC_OUTPUT(Makefile src/Makefile src/compat/Makefile isync.spec)
 
-if $ssl; then
+if test -n "$have_ssl_paths"; then
     AC_MSG_RESULT([
 Using SSL
 ])