swig-py: bump up required SWIG version to 1.3.40

It turned out that on SWIG 1.3.24 - 1.3.38, it causes syntax error in
svn_global.swg, and on SWIG 1.3.39, it produce broken C code. 

* build/ac-macros/swig.m4 (SVN_FIND_SWIG, SVN_DETERMINE_SWIG_OPTS):
  Replace least version number of SWIG from 1.3.24 to 1.3.40

* subversion/bindings/swig/INSTALL
  (BUILDING SWIG BINDINGS FOR SVN ON UNIX Step 1):
   It turned out SWIG 1.3.x except SWIG 1.3.40 does not work and
   1.3.40 is now tested (at least it passes the test suite).


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1928524 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/build/ac-macros/swig.m4 b/build/ac-macros/swig.m4
index 14a1093..16fa2ed 100644
--- a/build/ac-macros/swig.m4
+++ b/build/ac-macros/swig.m4
@@ -89,7 +89,7 @@
     # The major is passed straight through,
     # the minor is zero padded to two places,
     # and the patch level is zero padded to three places.
-    # e.g. 1.3.24 becomes 103024
+    # e.g. 1.3.40 becomes 103040
     SWIG_VERSION="`echo \"$SWIG_VERSION_RAW\" | \
                   $SED -e 's/[[^0-9\.]].*$//' \
                       -e 's/\.\([[0-9]]\)$/.0\1/' \
@@ -98,9 +98,9 @@
     AC_MSG_RESULT([$SWIG_VERSION_RAW])
     # If you change the required swig version number, don't forget to update:
     #   subversion/bindings/swig/INSTALL
-    if test ! -n "$SWIG_VERSION" || test "$SWIG_VERSION" -lt "103024"; then
+    if test ! -n "$SWIG_VERSION" || test "$SWIG_VERSION" -lt "103040"; then
       AC_MSG_WARN([Detected SWIG version $SWIG_VERSION_RAW])
-      AC_MSG_WARN([Subversion requires SWIG >= 1.3.24])
+      AC_MSG_WARN([Subversion requires SWIG >= 1.3.40])
     fi
   fi
 ])
@@ -206,7 +206,7 @@
                 else
                   SWIG_PY_OPTS="-no-such-option" # fool proof
                   SWIG_PY_ERRMSG="SWIG version is not suitable"
-                  AC_MSG_WARN([Subversion Python bindings for Python 2 require 1.3.24 <= SWIG < 4.0.0])
+                  AC_MSG_WARN([Subversion Python bindings for Python 2 require 1.3.40 <= SWIG < 4.0.0])
                 fi
               fi
             fi
diff --git a/subversion/bindings/swig/INSTALL b/subversion/bindings/swig/INSTALL
index 7e8b3bc..6a66f5b 100644
--- a/subversion/bindings/swig/INSTALL
+++ b/subversion/bindings/swig/INSTALL
@@ -82,11 +82,9 @@
 
     * We currently support SWIG versions 2.0.0 and later, with the
       following notes:
-      - SWIG 1.3.24 and later 1.3.x may work, but we do not test these
-        versions on our latest source code.
       - For Python 3 bindings, use SWIG 3.0.10 or later. (SWIG 4.0.0
         or later is supported as well.)
-      - For Python 2 bindings, use SWIG 2.x-3.x. (SWIG 4.0.0 or later
+      - For Python 2 bindings, use SWIG 1.3.40-3.x. (SWIG 4.0.0 or later
         is not supported as it lacks the '-classic' option.)
       - Note that SWIG 3.0.9 has some trouble with Python support.
         (See https://sourceforge.net/p/swig/news/2016/06/swig-3010-released/)