Making nettle-dev mandatory

configure

@@ -14736,11 +14736,31 @@ fi
 	# Put the nasty error message in config.log where it belongs
 	echo "$NETTLE_PKG_ERRORS" >&5
 
-	use_nettle=no
+	as_fn_error $? "Package requirements (nettle >= 2.4) were not met:
+
+$NETTLE_PKG_ERRORS
+
+Consider adjusting the PKG_CONFIG_PATH environment variable if you
+installed software in a non-standard prefix.
+
+Alternatively, you may set the environment variables NETTLE_CFLAGS
+and NETTLE_LIBS to avoid the need to call pkg-config.
+See the pkg-config man page for more details." "$LINENO" 5
 elif test $pkg_failed = untried; then
      	{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
 $as_echo "no" >&6; }
-	use_nettle=no
+	{ { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
+$as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
+as_fn_error $? "The pkg-config script could not be found or is too old.  Make sure it
+is in your PATH or set the PKG_CONFIG environment variable to the full
+path to pkg-config.
+
+Alternatively, you may set the environment variables NETTLE_CFLAGS
+and NETTLE_LIBS to avoid the need to call pkg-config.
+See the pkg-config man page for more details.
+
+To get pkg-config, see <http://pkg-config.freedesktop.org/>.
+See \`config.log' for more details" "$LINENO" 5; }
 else
 	NETTLE_CFLAGS=$pkg_cv_NETTLE_CFLAGS
 	NETTLE_LIBS=$pkg_cv_NETTLE_LIBS

configure.in

@@ -243,7 +243,7 @@ else
 	AC_MSG_RESULT(no)
 fi
 
-PKG_CHECK_MODULES(NETTLE, [nettle >= 2.4], [use_nettle=yes], [use_nettle=no])
+PKG_CHECK_MODULES(NETTLE, [nettle >= 2.4], [use_nettle=yes])
 
 if test "$use_nettle" = yes;then
 	CRYPTO_CFLAGS="$NETTLE_CFLAGS"